Autonomic Disorders
What Do You Need to Know?
- Neurogenic OH: ΔHR/ΔSBP <0.5 bpm/mmHg (validated) or HR rise <15 bpm despite large BP drop (bedside heuristic) = inadequate baroreflex → think MSA, PAF, diabetic neuropathy, amyloidosis
- POTS (2015 HRS): sustained HR rise ≥30 bpm in adults (≥40 bpm in adolescents) within 10 min of standing/tilt + orthostatic symptoms + absence of orthostatic hypotension. (A standing HR >120 may occur but is NOT a stand-alone criterion.) Young women, often post-viral.
- PAF vs MSA (heuristic, not standalone): both are α-synucleinopathies. Very low supine NE (fails to rise) suggests postganglionic failure (PAF); preserved supine NE with poor standing rise supports preganglionic/central failure (MSA). Interpret with autonomic testing, MIBG, exam, and longitudinal motor/cognitive signs.
- AAG: anti-ganglionic AChR antibodies (α3 nicotinic) — the ONE validated autoimmune autonomic antibody; titer correlates with severity
- Valsalva Phase IV: absent BP overshoot = sympathetic adrenergic failure — most tested autonomic reflex
- Autonomic dysreflexia: SCI above T6 + noxious stimulus below lesion → hypertension + bradycardia — medical emergency
- Preganglionic neurotransmitter: ALL autonomic preganglionic fibers use ACh at nicotinic receptors (sympathetic AND parasympathetic)
- OH definition: SBP ↓≥20 or DBP ↓≥10 within 3 min of standing — memorize the threshold
- Neurogenic vs non-neurogenic OH: neurogenic = BP drop WITHOUT compensatory HR rise (failed baroreflex) → MSA, PAF, PD, diabetic, amyloid, AAG
- POTS criteria (2015 HRS): sustained HR rise ≥30 bpm (≥40 bpm in adolescents) within 10 min of standing/tilt + orthostatic symptoms + absence of orthostatic hypotension; standing HR >120 is NOT a stand-alone criterion
- Pheo BP management: α-blockade FIRST (phenoxybenzamine/doxazosin) — never β-blocker first (unopposed α → hypertensive crisis)
- Autonomic dysreflexia (SCI ≥T6): severe HTN + headache + sweating/flushing above lesion + bradycardia → 1) sit upright, loosen constrictive clothing; 2) monitor BP frequently; 3) search trigger (bladder FIRST, then bowel, skin, other); 4) if SBP persistently ≥150 or markedly above baseline → short-acting antihypertensive (nitroglycerin paste, captopril, hydralazine, carefully administered immediate-release nifedipine per protocol). Avoid sublingual nifedipine.
- AAG antibody: anti-ganglionic AChR (α3 nicotinic) — subacute pandysautonomia (cholinergic + adrenergic failure); treat IVIG/PLEX/rituximab
- PAF (Bradbury-Eggleston): α-synucleinopathy with pure autonomic failure — may convert to PD/DLB/MSA over years
- MSA autonomic clue: early severe OH + urogenital failure + inspiratory stridor + parkinsonism/cerebellar = MSA
- Diabetic autonomic pentad: gastroparesis + erectile dysfunction + OH + asymptomatic hypoglycemia + silent MI
- Supine HTN in neurogenic OH: treat with short-acting agent at bedtime; never use long-acting antihypertensives
Clinical phenotype
- Young woman + palpitations/lightheadedness/brain fog on standing + HR↑ → POTS
- Early severe OH + inspiratory stridor + parkinsonism/cerebellar → MSA
- Slowly progressive pure autonomic failure WITHOUT motor/cognitive features → Pure Autonomic Failure (Bradbury-Eggleston)
- Subacute pandysautonomia (cholinergic + adrenergic) → Autoimmune Autonomic Ganglionopathy (AAG)
- Episodic HTN + headache + palpitations + diaphoresis + tremor → Pheochromocytoma
- SCI ≥T6 + severe HTN + flushing/sweating above lesion + bradycardia → Autonomic dysreflexia
- Gastroparesis + ED + OH + silent MI + asymptomatic hypoglycemia → Diabetic autonomic neuropathy
- Small fiber + autonomic + cardiomyopathy + GI + macroglossia → Amyloid autonomic neuropathy (TTR or AL)
- Sicca + sensory neuronopathy + autonomic failure → Sjögren autonomic ganglionopathy
- Ophthalmoplegia + ataxia + areflexia + autonomic instability → Miller Fisher / GBS variant
Testing / labs
- Tilt-table: BP drop WITHOUT HR rise → Neurogenic OH
- Tilt-table: sustained HR rise ≥30 bpm (≥40 bpm in adolescents) within 10 min + symptoms, NO orthostatic hypotension → POTS (2015 HRS)
- Valsalva Phase IV: absent BP overshoot → Sympathetic adrenergic failure
- Low supine NE (does not rise on standing) → supports postganglionic failure (PAF) — heuristic, not standalone; correlate with autonomic testing / MIBG / exam
- Preserved supine NE with inadequate rise on standing → supports preganglionic/central failure (MSA) — heuristic, not standalone
- Anti-ganglionic AChR (α3 nicotinic) antibody → AAG
- ↑ Plasma free metanephrines / 24-h urine metanephrines → Pheochromocytoma
- Congo red apple-green birefringence on biopsy → Amyloid autonomic neuropathy
- Reduced HR variability on deep breathing / R-R interval → Cardiovagal (parasympathetic) failure
- QSART / TST anhidrosis pattern → Sudomotor (postganglionic sympathetic) failure
Treatment / pearls
- Midodrine (α1 agonist) → Neurogenic OH first-line pressor
- Droxidopa (NE precursor) → Neurogenic OH (PAF, MSA, PD)
- Fludrocortisone (mineralocorticoid) → Volume expansion in OH
- Pyridostigmine → Mild OH — augments residual sympathetic ganglionic transmission
- Phenoxybenzamine / doxazosin BEFORE β-blocker → Pheochromocytoma (avoid unopposed α)
- Increased salt + fluids + compression + recumbent-to-upright exercise → POTS first-line
- Low-dose propranolol / ivabradine → POTS rate control
- IVIG / PLEX / rituximab → AAG
- Sit upright, loosen clothing, monitor BP; search trigger (bladder FIRST, then bowel/skin); if SBP ≥150 or markedly above baseline → short-acting antihypertensive (nitro paste, captopril, hydralazine, careful IR nifedipine per protocol — NOT SL nifedipine) → Autonomic dysreflexia
- Abdominal binder + HOB elevation + avoid hot environments → Non-pharmacologic OH bundle
- Short-acting antihypertensive at bedtime only → Supine HTN in neurogenic OH
Autonomic Nervous System — Quick Review
Sympathetic vs Parasympathetic
| Feature | Sympathetic | Parasympathetic |
|---|
| Origin | T1–L2 (intermediolateral cell column) | Cranial (III, VII, IX, X) + Sacral (S2–S4) |
| Preganglionic fiber | Short; ACh at nicotinic receptors | Long; ACh at nicotinic receptors |
| Postganglionic fiber | Long; norepinephrine (except sweat glands = ACh) | Short; acetylcholine (muscarinic receptors) |
| Ganglia | Paravertebral (sympathetic chain) + prevertebral (celiac, superior/inferior mesenteric) | Near or within target organ |
| Heart | ↑ HR, ↑ contractility (β1) | ↓ HR, ↓ conduction (muscarinic M2) |
| Pupils | Mydriasis (dilator pupillae, α1) | Miosis (sphincter pupillae, M3) |
| GI | ↓ Motility, sphincter contraction | ↑ Motility, sphincter relaxation |
| Bladder | Detrusor relaxation (β2/3), sphincter contraction (α1) | Detrusor contraction (M3), sphincter relaxation |
| Sweat glands | Eccrine: sympathetic cholinergic (ACh, muscarinic) | No innervation |
Key Anatomic Points
- Adrenal medulla: modified sympathetic ganglion — preganglionic fibers synapse directly; releases epinephrine (80%) + norepinephrine (20%)
- Sympathetic sweat glands: the ONE exception — sympathetic postganglionic fibers that release ACh (not NE)
- Horner syndrome pathway: 3-neuron arc — 1st order: hypothalamus → C8–T2 ciliospinal center of Budge (intermediolateral column); 2nd order: ciliospinal center → superior cervical ganglion (passes over lung apex); 3rd order: SCG → along ICA → cavernous sinus → eye via long ciliary nerves
- Vagus nerve (CN X): provides ~75% of all parasympathetic innervation; heart, lungs, GI (to splenic flexure)
- ALL preganglionic fibers (sympathetic AND parasympathetic) use ACh at nicotinic receptors — this is why ganglionic AChR antibodies cause pandysautonomia
- Sympathetic postganglionic = NE everywhere EXCEPT sweat glands (ACh, muscarinic) — classic board question
Orthostatic Hypotension
Definition & Criteria
- Orthostatic hypotension: SBP drop ≥20 mmHg OR DBP drop ≥10 mmHg within 3 minutes of standing (or head-up tilt)
- Initial OH: transient drop within 15 seconds of standing (not sustained) — benign
- Delayed OH: BP drop after 3 minutes but within 10 minutes — may be early neurogenic OH
Neurogenic vs Non-Neurogenic OH
| Feature | Neurogenic OH | Non-Neurogenic OH |
|---|
| ΔHR / ΔSBP ratio (validated primary criterion) | <0.5 bpm/mmHg | >0.5 bpm/mmHg |
| HR response to standing (supportive bedside heuristic) | <15 bpm rise despite large BP drop | >15 bpm rise (appropriate) |
| Supine NE | Low (PAF) or fails to rise on standing (MSA) | Normal |
| Causes | MSA, PAF, PD, diabetic neuropathy, amyloidosis, AAG | Dehydration, hemorrhage, medications, adrenal insufficiency, sepsis |
| Supine hypertension | Common (loss of baroreflex modulation) | Uncommon |
| Valsalva Phase IV | Absent overshoot | Normal overshoot |
Common Medications Causing OH
- Antihypertensives (α-blockers, diuretics), dopaminergic agents (levodopa, dopamine agonists), TCAs, antipsychotics, nitrates, PDE5 inhibitors
Supine Hypertension
- Defined as SBP ≥140 and/or DBP ≥90 mmHg while supine
- Present in >50% of neurogenic OH patients — makes treatment challenging
- Management: elevate head of bed 10–15° (~6–9 inches), avoid supine position during day, low-dose transdermal nitroglycerin patch at bedtime (removed in AM)
Treatment of Orthostatic Hypotension
| Approach | Intervention | Mechanism / Notes |
|---|
| Non-pharmacologic | Compression stockings (waist-high) | Reduces venous pooling; abdominal binders more effective than stockings alone |
| Increased salt (6–10 g/day) + fluid (2–3 L/day) | Volume expansion; first step always |
| Counter-pressure maneuvers | Leg crossing, squatting, muscle tensing during symptoms |
| Head-up tilt sleeping (10–15°) | Reduces nocturnal supine hypertension + natriuresis; preserves morning volume |
| Pharmacologic | Midodrine | α1-agonist; peripheral vasoconstriction; avoid within 4 h of bedtime (supine HTN); do NOT give supine |
| Droxidopa (Northera) | Norepinephrine precursor; FDA-approved for neurogenic OH; converted to NE by DOPA decarboxylase |
| Fludrocortisone | Mineralocorticoid; volume expansion + ↑ vascular α-receptor sensitivity; watch K+, edema, supine HTN |
| Pyridostigmine | AChE inhibitor; enhances ganglionic transmission; modest effect; less supine hypertension |
- HR increase <15 bpm on standing = neurogenic OH (baroreflex failure) — the single most important bedside clue
- Droxidopa is the only FDA-approved NE precursor for neurogenic OH — know the drug name
- Midodrine is an α1-agonist — last dose ≥4 hours before bedtime to avoid supine hypertension
Postural Tachycardia Syndrome (POTS)
Diagnostic Criteria
- Adults: sustained HR increase ≥30 bpm within 10 minutes of standing/tilt
- Adolescents (12–19): sustained HR increase ≥40 bpm
- Orthostatic symptoms required (lightheadedness, palpitations, tremor, exercise intolerance, brain fog) AND absence of orthostatic hypotension (SBP drop <20 mmHg / DBP <10 mmHg)
- Symptoms typically present ≥6 months
- Note: a standing HR >120 bpm may occur but is NOT a stand-alone diagnostic criterion (2015 HRS consensus)
Demographics
- Female predominance (5:1), age 15–50
- Common triggers: post-viral (including post-COVID), post-surgical, post-concussion
Subtypes
| Subtype | Mechanism | Key Features |
|---|
| Neuropathic | Partial small fiber neuropathy → lower limb sympathetic denervation | Decreased sweating in legs (QSART abnormal distally); blood pooling in lower extremities |
| Hyperadrenergic | Excessive sympathetic drive | Standing NE >600 pg/mL; prominent palpitations, tremor, anxiety, orthostatic hypertension (SBP rise ≥10 mmHg on standing); may have mast cell activation |
| Hypovolemic | Low circulating blood volume | Low plasma volume, low renin-aldosterone; inadequate volume for upright posture |
Associated Conditions
- Ehlers-Danlos syndrome / joint hypermobility — high comorbidity; connective tissue laxity → venous pooling
- Mast cell activation syndrome (MCAS), autoimmune disorders, small fiber neuropathy, chronic fatigue syndrome
Treatment
| Line | Intervention | Notes |
|---|
| Non-pharmacologic (first) | Fluid 2–3 L/day, salt 10–12 g/day | Volume expansion is cornerstone |
| Compression garments (waist-high) | Abdominal binder most effective |
| Graduated exercise program | Start recumbent (rowing, swimming); avoid upright exercise initially |
| Pharmacologic | Propranolol (10–20 mg) | Low-dose β-blocker; controls HR without worsening BP |
| Midodrine | α1-agonist; reduces venous pooling |
| Fludrocortisone | Volume expansion |
| Ivabradine | If-channel blocker; lowers HR without BP effect; emerging use |
| Pyridostigmine | AChE inhibitor; enhances ganglionic neurotransmission |
- POTS is NOT a diagnosis of exclusion — must meet specific HR criteria AND exclude orthostatic hypotension
- Standing NE >600 pg/mL = hyperadrenergic subtype — the one with the most dramatic palpitations and tremor
- Exercise reconditioning is the most effective long-term treatment — start recumbent, progress slowly
Pure Autonomic Failure (PAF)
Key Features
| Feature | Details |
|---|
| Pathology | α-synucleinopathy; Lewy bodies in autonomic ganglia (peripheral) |
| Presentation | Severe orthostatic hypotension, supine hypertension, anhidrosis, constipation, urinary retention, erectile dysfunction |
| CNS involvement | None — no parkinsonism, no cerebellar signs, no cognitive decline |
| Supine NE | Very low (<100 pg/mL) — supports postganglionic failure (heuristic; not a standalone discriminator — combine with autonomic testing, MIBG, exam) |
| Standing NE | Fails to rise appropriately |
| MIBG cardiac scan | Reduced uptake (postganglionic cardiac sympathetic denervation) |
| Onset | Insidious, middle-aged to elderly |
Phenoconversion Risk
- Approximately one-third of PAF patients phenoconvert within 4 years (Kaufmann 2017), with rates rising to ~50% with longer follow-up — convert to MSA, PD, or DLB; longitudinal surveillance needed
- Predictors of conversion: RBD, cognitive changes, subtle motor signs, abnormal DaTscan
- If parkinsonism develops → reclassify as PD; if cerebellar signs → MSA-C; if early dementia → DLB
PAF vs MSA vs PD: Autonomic Comparison
| Feature | PAF | MSA | PD |
|---|
| OH severity | Severe | Severe (often >30 mmHg drop) | Mild–moderate (usually later) |
| Supine NE | Very low | Normal or mildly low | Normal or mildly low |
| Standing NE | Fails to rise (postganglionic) | Fails to rise (preganglionic) | Variable |
| MIBG cardiac scan | Abnormal (postganglionic) | Normal (preganglionic) | Abnormal (postganglionic) |
| CNS signs | None | Parkinsonism ± cerebellar | Parkinsonism |
| Lesion | Peripheral (postganglionic) | Central (preganglionic) | Both |
- PAF = peripheral α-synucleinopathy with isolated autonomic failure; if motor/cerebellar/cognitive signs appear → reclassify as MSA, PD, or DLB
- Plasma NE pattern is a heuristic, not a standalone discriminator: very low supine NE supports a postganglionic lesion (PAF, diabetic neuropathy); preserved supine NE that fails to rise supports a preganglionic lesion (MSA). Interpret with autonomic testing, MIBG, exam, and longitudinal motor/cognitive features.
- MIBG scan: abnormal in PAF & PD (postganglionic denervation); normal in MSA (preganglionic lesion) — differentiates MSA from PAF/PD
Multiple System Atrophy — Autonomic Perspective
MSA Subtypes
| Subtype | Predominant Motor | Autonomic Failure |
|---|
| MSA-P (parkinsonian) | Akinetic-rigid parkinsonism; poor levodopa response | Severe; early and prominent |
| MSA-C (cerebellar) | Cerebellar ataxia, dysarthria, nystagmus | Severe; early and prominent |
MDS-MSA 2022 Diagnostic Criteria
- Clinically established MSA requires severe autonomic failure (OH ≥20/10 mmHg within 3 min OR unexplained urinary urge incontinence with ED in males <60) + poor-levodopa-response parkinsonism (MSA-P) OR cerebellar syndrome (MSA-C) + ≥2 supportive features
- Adds “clinically probable MSA” (less stringent autonomic threshold) and “possible prodromal MSA” (RBD, isolated autonomic failure, or subtle motor signs preceding full syndrome) categories
Autonomic Features of MSA
- Orthostatic hypotension: severe (often >30 mmHg SBP drop); early in disease; with supine hypertension
- Urogenital: urinary retention/incontinence (early); erectile dysfunction often the earliest symptom in males
- Stridor: laryngeal abductor paralysis — nocturnal inspiratory stridor; can cause sudden death; may require tracheostomy or CPAP
- Cold, purple hands: vasomotor dysfunction; characteristic
MSA vs PD: Autonomic Comparison
| Feature | MSA | PD |
|---|
| OH severity | Severe, early | Mild–moderate, later in course |
| Urinary dysfunction | Early, prominent (retention + incontinence) | Later, milder (urgency/frequency) |
| Stridor | Present (≥30%); potentially fatal | Absent |
| Erectile dysfunction | Early, often first symptom | Present, usually later |
| Supine NE | Normal (preganglionic) | Normal or low (postganglionic component) |
| MIBG cardiac scan | Normal | Abnormal |
| Levodopa response | Poor or transient | Robust, sustained |
| Progression | Rapid (survival 6–10 yr) | Slow (survival >15 yr) |
Red Flags for MSA (vs PD)
- Early severe autonomic failure (≤5 yr of motor onset)
- Stridor (laryngeal abductor paralysis)
- Cold, purple hands
- Anterocollis (disproportionate neck flexion)
- Rapid progression; poor/transient levodopa response
- Early recurrent falls
Imaging
- Hot cross bun sign: cruciform hyperintensity in pons on T2 MRI — selective loss of pontine neurons/myelinated fibers (MSA-C)
- Putaminal slit sign: hyperintense lateral putaminal rim on T2 (MSA-P)
- Putaminal atrophy with hypointensity on T2 (iron deposition)
- Stridor in MSA = laryngeal abductor paralysis — can cause sudden death during sleep; may require tracheostomy
- Erectile dysfunction is often the earliest symptom of MSA in males — precedes motor by years
- MIBG scan normal in MSA (preganglionic) vs abnormal in PD/PAF (postganglionic) — key differentiator
Autoimmune Autonomic Ganglionopathy (AAG)
Overview
| Feature | Details |
|---|
| Antibody | Anti-ganglionic AChR (α3 subunit of nicotinic acetylcholine receptor) |
| Onset | Acute/subacute pandysautonomia over weeks to months |
| OH | Severe orthostatic hypotension |
| Sicca symptoms | Dry eyes, dry mouth (parasympathetic involvement) |
| GI | Severe gastroparesis, constipation, ileus |
| Urinary | Urinary retention (neurogenic bladder) |
| Pupils | Fixed, dilated (tonic pupils) — parasympathetic denervation |
| Sudomotor | Anhidrosis (global) |
| Motor/sensory | None — pure autonomic |
AAG vs Guillain-Barré Syndrome
| Feature | AAG | GBS |
|---|
| Motor weakness | Absent | Ascending paralysis |
| Sensory loss | Absent | Variable (paresthesias common) |
| Autonomic failure | Predominant (pandysautonomia) | Present but not primary |
| Antibody | Anti-ganglionic AChR | Anti-ganglioside (GM1, GQ1b, etc.) |
| CSF | Normal | Albuminocytologic dissociation |
| Analogy | “Autonomic GBS” | Motor/sensory predominant |
Paraneoplastic Association
- SCLC (small cell lung cancer), thymoma — always screen for malignancy
- Can overlap with other paraneoplastic antibodies
Diagnosis & Treatment
- Antibody titer correlates with disease severity — higher titer = more severe dysautonomia
- Autonomic testing: widespread sympathetic + parasympathetic failure on CASS
- Treatment: IVIg, plasma exchange (PLEX), rituximab, corticosteroids; treat underlying malignancy if paraneoplastic
- Some patients have chronic/relapsing course; may need maintenance immunotherapy
- Anti-ganglionic AChR Ab is the ONE validated autoimmune autonomic antibody — titer directly correlates with severity
- AAG = “autonomic GBS” — pure pandysautonomia without motor or sensory involvement
- Fixed dilated pupils + dry eyes/mouth + GI dysmotility + severe OH + urinary retention in an acute/subacute onset → think AAG
Autonomic Testing
Cardiovagal (Parasympathetic) Tests
| Test | What It Measures | Normal Response | Abnormal Indicates |
|---|
| Deep breathing (HR variability) | Cardiovagal function | HR varies ≥15 bpm with deep breathing at 6 breaths/min | ↓ HR variability = vagal neuropathy |
| Valsalva ratio | Cardiovagal + adrenergic | Longest RR interval (Phase IV) / shortest RR interval (Phase II); age-adjusted; ≥1.21 is the commonly cited Mayo lower limit; declines with age | Low ratio = cardiovagal failure |
| Head-up tilt | Integrated baroreflex | Stable BP with appropriate HR increase | OH ± inadequate HR response |
Valsalva Maneuver — Four Phases
| Phase | BP | HR | Mechanism |
|---|
| Phase I | ↑ | Transient ↓ | Thoracic compression → aortic squeezing |
| Phase II early | ↓ | ↑ | ↓ Venous return → ↓ CO → baroreflex-mediated tachycardia |
| Phase II late | Recovery toward baseline | Sustained ↑ | Sympathetic vasoconstriction (if intact adrenergic function) |
| Phase III | Brief ↓ | — | Release of strain → transient ↓ BP |
| Phase IV | BP overshoot | Reflex bradycardia | Increased venous return into vasoconstricted bed → overshoot; baroreflex slows HR |
- Absent Phase II late recovery = sympathetic (adrenergic) failure
- Absent Phase IV overshoot = sympathetic (adrenergic) failure — the most tested Valsalva abnormality on boards
- Low Valsalva ratio (Phase IV bradycardia absent) = cardiovagal failure
Sudomotor (Sympathetic Cholinergic) Tests
| Test | What It Assesses | Key Points |
|---|
| QSART (quantitative sudomotor axon reflex test) | Postganglionic sympathetic sudomotor function | Acetylcholine iontophoresis stimulates axon reflex; measures sweat volume at 4 sites (forearm, proximal/distal leg, foot) |
| TST (thermoregulatory sweat test) | Pre + postganglionic (entire sympathetic pathway) | Indicator powder changes color with sweat; whole-body map; can localize central vs peripheral |
| Sympathetic skin response (SSR) | Sudomotor sympathetic pathway | EDA change to stimuli; highly variable; least reliable |
Localizing Sudomotor Lesions
- TST abnormal + QSART abnormal = postganglionic lesion (PAF, peripheral neuropathy)
- TST abnormal + QSART normal = preganglionic lesion (MSA, spinal cord)
Plasma Catecholamines
| Condition | Supine NE | Standing NE | Interpretation |
|---|
| Normal | 100–350 pg/mL | ↑ ≥2× supine | Intact sympathetic outflow |
| PAF | Very low (<100) | Fails to rise | Postganglionic neuron loss |
| MSA | Normal | Fails to rise adequately | Preganglionic (central) failure |
| POTS (hyperadrenergic) | Normal | >600 pg/mL (excessive rise) | Sympathetic overactivation |
CASS (Composite Autonomic Severity Score)
- Standardized scoring combining: sudomotor (0–3) + cardiovagal (0–3) + adrenergic (0–4) = total 0–10
- Used to quantify overall autonomic failure severity and track progression
- Absent Valsalva Phase IV overshoot = adrenergic (sympathetic) failure — highest-yield autonomic testing fact
- QSART = postganglionic; TST = entire pathway; TST abnormal + QSART normal = preganglionic lesion
- Plasma NE pattern is a heuristic, not standalone: low supine NE supports postganglionic (PAF); preserved supine NE that fails to rise supports preganglionic (MSA) — combine with autonomic testing, MIBG, exam
Neurogenic Bladder & Sexual Dysfunction
Bladder Innervation
| Component | Innervation | Nerve | Spinal Level | Function |
|---|
| Detrusor muscle | Parasympathetic (M3) | Pelvic nerve | S2–S4 | Contraction → voiding |
| Internal sphincter | Sympathetic (α1) | Hypogastric nerve | T11–L2 | Contraction → storage |
| External sphincter | Somatic (nicotinic) | Pudendal nerve | S2–S4 (Onuf nucleus, S1–S3, predominantly S2) | Voluntary contraction → continence |
UMN vs LMN Bladder
| Feature | UMN Bladder (Spastic) | LMN Bladder (Flaccid) |
|---|
| Lesion level | Above sacral cord (suprapontine or spinal cord) | Sacral cord (S2–S4), cauda equina, or peripheral nerves |
| Detrusor | Hyperactive (uninhibited contractions) | Areflexic (no contraction) |
| Capacity | Small (reduced) | Large (distended) |
| Sensation | May be preserved (urgency) | Absent |
| Voiding pattern | Urgency, frequency, urge incontinence | Overflow incontinence, straining |
| Post-void residual | Low (if no DSD) or high (if DSD present) | High (incomplete emptying) |
| DSD | Present if lesion between pons and sacral cord | Absent |
| Treatment | Antimuscarinics (oxybutynin, solifenacin), β3-agonist (mirabegron), botulinum toxin | CIC (clean intermittent catheterization) |
Detrusor-Sphincter Dyssynergia (DSD)
- Simultaneous detrusor contraction + external sphincter contraction (should relax)
- Occurs with spinal cord lesions between pons and sacral cord (pontine micturition center coordinates; suprapontine lesions have synergistic voiding)
- Results in high bladder pressures → risk of hydronephrosis, UTIs, renal damage
- Treatment: CIC + antimuscarinics; botulinum toxin to sphincter; alpha-blockers
Common Neurologic Causes
| Condition | Bladder Type | Key Features |
|---|
| MS | UMN (most common) | Urgency, frequency, urge incontinence; DSD common with spinal plaques |
| Spinal cord injury | UMN (above conus) or LMN (conus/cauda) | DSD if between pons and sacral cord; spinal shock initially → areflexia then spastic |
| Diabetic neuropathy | LMN | Insidious; decreased sensation → large-capacity, overflow incontinence |
| Cauda equina syndrome | LMN | Urinary retention (often early) + saddle anesthesia + bilateral leg weakness/pain |
| MSA | Mixed (central + peripheral) | Early urinary retention/incontinence — disproportionate to motor severity |
Sexual Dysfunction
- Erection: parasympathetic S2–S4 (pelvic nerve); Point & Shoot mnemonic — Parasympathetic = Point (erection), Sympathetic = Shoot (ejaculation)
- Ejaculation: sympathetic T11–L2 (hypogastric nerve)
- Erectile dysfunction may be the earliest autonomic symptom in diabetes and MSA
- Always consider medications (antihypertensives, SSRIs, antipsychotics) as cause
- DSD only occurs with lesions between pons and sacral cord — suprapontine lesions (stroke, PD) cause urgency but NOT DSD
- Cauda equina: urinary retention is a hallmark — LMN bladder + saddle anesthesia = surgical emergency
- “Point and Shoot”: Parasympathetic = erection; Sympathetic = ejaculation
Specific Autonomic Conditions — Quick Reference
Autonomic Dysreflexia
| Feature | Details |
|---|
| Who | Spinal cord injury at or above T6 |
| Trigger | Noxious stimulus below lesion (bladder distension #1, bowel impaction, skin pressure, UTI) |
| Mechanism | Cord lesion blocks descending supraspinal inhibition of below-lesion sympathetic outflow → uninhibited sympathetic discharge → vasoconstriction + HTN. Intact vagal baroreflex from carotid/aortic baroreceptors → reflex bradycardia (and vasodilation/flushing above the lesion only, where sympathetic supply is intact and can be inhibited) |
| Symptoms above lesion | Headache (pounding), flushing, sweating |
| Symptoms below lesion | Pallor, piloerection, cool skin |
| Vitals | Hypertension (SBP can exceed 200) + reflex bradycardia |
| Emergency management | 1) Sit upright (lower BP); 2) Identify & remove noxious stimulus (catheterize bladder, disimpact bowel); 3) If persistent: topical nitroglycerin paste (first-line pharmacologic), captopril 25 mg SL, hydralazine IV; AVOID immediate-release nifedipine (risk of precipitous BP drop) |
Autonomic dysreflexia is a medical emergency — SBP can exceed 200–300 mmHg, risking stroke, seizure, retinal hemorrhage, or death. Immediate identification and removal of the noxious stimulus is the priority.
Complex Regional Pain Syndrome (CRPS)
| Feature | CRPS Type I (RSD) | CRPS Type II (Causalgia) |
|---|
| Nerve injury | No identifiable nerve lesion | Defined peripheral nerve injury |
| Trigger | Fracture, surgery, immobilization | Nerve trauma (partial injury common) |
| Presentation | Burning pain, allodynia, hyperalgesia + vasomotor changes (temperature/color asymmetry) + sudomotor changes (edema, sweating) + trophic changes (skin, nail, hair) |
Budapest Criteria (Requires All 4)
- 1. Continuing pain disproportionate to inciting event
- 2. ≥1 symptom in 3 of 4 categories: sensory (hyperesthesia/allodynia), vasomotor (temperature/color asymmetry), sudomotor/edema (edema/sweating changes), motor/trophic (weakness/tremor/dystonia/trophic changes)
- 3. ≥1 sign at examination in ≥2 categories
- 4. No other diagnosis better explains the findings
CRPS Treatment
- Physical/occupational therapy (cornerstone), mirror therapy, graded motor imagery
- Pharmacologic: gabapentin/pregabalin, TCAs, corticosteroids (early, short course), bisphosphonates
- Interventional: sympathetic nerve blocks, spinal cord stimulation, intrathecal baclofen (for dystonia)
Baroreflex Failure
| Feature | Details |
|---|
| Cause | Damage to baroreceptors or NTS (nucleus tractus solitarius) — post-neck surgery, radiation, bilateral carotid body tumors |
| Presentation | Labile hypertension with tachycardia (volatile surges); may alternate with hypotension |
| Key distinction | Hypertensive crises with tachycardia (unlike pheochromocytoma: also episodic but catecholamines elevated) |
| Treatment | Clonidine (central α2-agonist to reduce sympathetic outflow); benzodiazepines for acute crisis |
Hyperhidrosis
| Type | Distribution | Key Features |
|---|
| Primary focal | Axillary, palmar, plantar, craniofacial | Onset in adolescence; bilateral, symmetric; worse with stress; family history common |
| Secondary generalized | Generalized/diffuse | Think: autonomic neuropathy, lymphoma, pheochromocytoma, carcinoid, hyperthyroidism, menopause, medications |
Familial Dysautonomia (Riley-Day Syndrome, HSAN-III)
| Feature | Details |
|---|
| Classification | HSAN-III (hereditary sensory and autonomic neuropathy, type III) |
| Gene | IKBKAP/ELP1 (elongator complex protein 1) |
| Inheritance | Autosomal recessive |
| Population | Ashkenazi Jewish (carrier frequency ~1:30) |
| Pathology | Loss of sensory and autonomic neurons (small fiber > large fiber) |
| Classic findings | Absent fungiform papillae (smooth tongue), absence of tears (alacrima), orthostatic hypotension with labile BP, episodic hypertensive crises with vomiting (“dysautonomic crisis”), and inappropriate HR responses (often tachycardic but uncoupled from BP), pain/temperature insensitivity |
| Pharmacologic sign | Methacholine eye drops produce miosis (cholinergic denervation supersensitivity) — classic Riley-Day pharmacologic sign |
| Diagnosis | Genetic testing; absent axon flare with intradermal histamine injection |
| Prognosis | Median survival ~40 years; recurrent aspiration pneumonia is major morbidity |
Horner Syndrome
- Triad: miosis + ptosis + anhidrosis (ipsilateral)
- 3-neuron sympathetic pathway: 1st order: hypothalamus → C8–T2 ciliospinal center of Budge (intermediolateral column); 2nd order: ciliospinal center → superior cervical ganglion (passes over lung apex); 3rd order: SCG → along ICA → cavernous sinus → eye via long ciliary nerves
- Apraclonidine 0.5–1% (now the preferred bedside test): weak α1 / strong α2 agonist; in Horner syndrome, postsynaptic α1 receptor upregulation causes reversal of anisocoria — the Horner pupil dilates (and ptosis improves), while the normal pupil does not. Avoid in infants <6 months (CNS depression). Confirms Horner but does NOT localize lesion order
- Cocaine test (blocks NE reuptake): fails to dilate Horner pupil (confirms Horner)
- Hydroxyamphetamine test: dilates = preganglionic (1st/2nd order); fails to dilate = postganglionic (3rd order)
- Cross-referenced in neuro-ophthalmology
- Autonomic dysreflexia: SCI ≥T6 + noxious stimulus below lesion → hypertension + bradycardia; bladder distension is the #1 trigger — catheterize first
- Riley-Day: Ashkenazi Jewish + absent fungiform papillae + alacrima + orthostatic hypotension = IKBKAP/ELP1 mutation
- Baroreflex failure: post-neck surgery/radiation + volatile hypertensive surges with tachycardia — treat with clonidine
- CRPS Type I (no nerve injury) vs Type II (identifiable nerve injury) — same clinical phenotype, different etiology
hATTR Amyloidosis (Familial Amyloid Polyneuropathy)
Overview
| Feature | Details |
|---|
| Gene | TTR (transthyretin); autosomal dominant |
| Most common variant | Val30Met (V30M) — endemic clusters in Portugal, Sweden, Japan |
| Clinical tetrad | Autonomic failure + length-dependent sensorimotor neuropathy + restrictive cardiomyopathy + bilateral carpal tunnel syndrome |
| Autonomic features | Severe OH, gastroparesis, diarrhea/constipation alternation, ED, neurogenic bladder, sudomotor failure |
| Diagnosis | Genetic testing for TTR mutation; nerve/abdominal fat-pad biopsy with Congo red (apple-green birefringence); cardiac PYP scan |
FDA-Approved Disease-Modifying Therapies
| Drug | Class / Mechanism | Notes |
|---|
| Tafamidis | TTR stabilizer (small molecule) | Oral; stabilizes tetramer; cardiomyopathy + polyneuropathy indications |
| Patisiran | siRNA (lipid nanoparticle) | IV every 3 weeks; silences hepatic TTR mRNA |
| Inotersen / Eplontersen | Antisense oligonucleotide (ASO) | Inotersen SC weekly (thrombocytopenia risk); eplontersen newer, monthly |
| Vutrisiran | Next-generation siRNA | SC every 3 months; longer dosing interval than patisiran |
| Acoramidis | TTR stabilizer (newer) | Oral; high TTR stabilization potency |
- Bilateral CTS + cardiomyopathy + autonomic + sensorimotor neuropathy in middle-aged adult → think hATTR
- Two therapeutic strategies: silence TTR production (patisiran, vutrisiran, inotersen, eplontersen) vs stabilize TTR tetramer (tafamidis, acoramidis)
Reflex (Neurally Mediated) Syncope
Subtypes
| Subtype | Mechanism / Trigger | Key Features |
|---|
| Vasovagal / neurocardiogenic | Emotional stress, prolonged standing, pain | Prodrome (nausea, diaphoresis, warmth, tunnel vision); post-syncope fatigue; quick recovery |
| Situational | Cough, micturition, defecation, swallow | Stereotyped trigger; vagal afferent → reflex hypotension ± bradycardia |
| Carotid sinus hypersensitivity | Carotid sinus pressure (shaving, tight collars, head turning) | Elderly males; cardioinhibitory or vasodepressor response |
Head-Up Tilt Test Responses
- Cardioinhibitory: bradycardia/asystole predominates → consider pacemaker if recurrent
- Vasodepressor: BP drop without significant bradycardia
- Mixed: both BP and HR drop
- Reflex syncope has a prodrome; cardiac syncope is usually sudden and without warning — key distinction
- Tilt-table response (cardioinhibitory vs vasodepressor vs mixed) guides therapy
Diabetic Autonomic Neuropathy
Clinical Features
| System | Manifestation |
|---|
| Cardiovascular | Resting tachycardia, fixed HR (loss of variability), orthostatic hypotension, silent ischemia/MI, increased perioperative mortality |
| GI | Gastroparesis (nausea, bloating, early satiety), diarrhea (often nocturnal), constipation, fecal incontinence |
| Metabolic | Hypoglycemia unawareness (loss of adrenergic warning symptoms) |
| Genitourinary | Erectile dysfunction (often earliest), retrograde ejaculation, neurogenic bladder (large-capacity, overflow) |
| Sudomotor | Distal anhidrosis with compensatory truncal hyperhidrosis; gustatory sweating |
| Pupillary | Reduced pupillary light reflex amplitude; sluggish |
Management
- Glycemic control reduces but does not reverse established autonomic neuropathy (DCCT/EDIC)
- Symptomatic: midodrine/droxidopa for OH; prokinetics (metoclopramide, erythromycin) for gastroparesis; PDE5 inhibitors for ED
- Silent MI + resting tachycardia + fixed HR in a diabetic = cardiac autonomic neuropathy — major mortality predictor
- Hypoglycemia unawareness in long-standing diabetes is a hallmark autonomic complication
Other Autoimmune & Paraneoplastic Autonomic Neuropathies
Sjögren Autonomic Neuropathy
- Sicca symptoms (dry eyes, dry mouth) + small-fiber/autonomic neuropathy
- Anti-Ro (SSA) / anti-La (SSB) antibodies; biopsy of minor salivary glands confirms
- Can present as Adie tonic pupil, length-dependent autonomic failure, or pandysautonomia
- Treatment: pilocarpine/cevimeline for sicca; immunotherapy (steroids, IVIg, rituximab) for severe neuropathy
Paraneoplastic Autonomic Neuropathies
- Anti-Hu (ANNA-1): SCLC; sensory neuronopathy + autonomic failure + GI dysmotility (chronic intestinal pseudo-obstruction)
- Anti-CRMP-5 (CV2): SCLC, thymoma; mixed CNS/PNS + autonomic features
- Always screen for occult malignancy when subacute pandysautonomia presents in older smoker
- Sicca + autonomic neuropathy + anti-Ro/La → Sjögren autonomic neuropathy
- Anti-Hu = SCLC + sensory neuronopathy + autonomic failure — classic paraneoplastic triad
References
- Freeman R, Wieling W, Axelrod FB, et al. Consensus statement on the definition of orthostatic hypotension, neurally mediated syncope and the postural tachycardia syndrome. Clin Auton Res. 2011;21(2):69-72.
- Gibbons CH, Schmidt P, Biaggioni I, et al. The recommendations of a consensus panel for the screening, diagnosis, and treatment of neurogenic orthostatic hypotension and associated supine hypertension. J Neurol. 2017;264(8):1567-1582.
- Vernino S, Hopkins S, Wang Z. Autonomic ganglia, acetylcholine receptor antibodies, and autoimmune ganglionopathy. Auton Neurosci. 2009;146(1-2):3-7.
- Vernino S, Low PA, Fealey RD, et al. Autoantibodies to ganglionic acetylcholine receptors in autoimmune autonomic neuropathies. N Engl J Med. 2000;343(12):847-855.
- Benarroch EE. The autonomic nervous system: basic anatomy and physiology. Continuum (Minneap Minn). 2020;26(1):13-30.
- Fanciulli A, Wenning GK. Multiple-system atrophy. N Engl J Med. 2015;372(3):249-263.
- Kaufmann H, Norcliffe-Kaufmann L, Palma JA. Baroreflex dysfunction. N Engl J Med. 2020;382(2):163-178.
- Chelimsky TC, et al. Autonomic testing. In: Clinical Autonomic Disorders. 3rd ed. Lippincott Williams & Wilkins; 2008.
- Sheldon RS, Grubb BP, Olshansky B, et al. 2015 Heart Rhythm Society expert consensus statement on the diagnosis and treatment of postural tachycardia syndrome. Heart Rhythm. 2015;12(6):e41-e63.
- Harden RN, Bruehl S, Perez RS, et al. Validation of proposed diagnostic criteria (the “Budapest Criteria”) for complex regional pain syndrome. Pain. 2010;150(2):268-274.
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