Rapidly Progressive Dementias
Rapidly Progressive Dementias
What Do You Need to Know?
- Definition: Subacute cognitive decline progressing to severe dementia within weeks to months (typically <1–2 years from onset) — far faster than typical neurodegenerative dementias
- Prion disease (sCJD) is the most tested RPD on boards: rapidly progressive dementia + myoclonus + akinetic mutism; MRI DWI cortical ribboning; CSF RT-QuIC (most specific test); EEG periodic sharp wave complexes; mean survival ~5 months
- Autoimmune encephalitis is the most important treatable RPD: anti-NMDAR, anti-LGI1, anti-CASPR2, anti-GABA-B — always send serum + CSF antibody panels
- Boards love reversible causes: autoimmune encephalitis, Hashimoto encephalopathy (SREAT), CNS vasculitis, Whipple disease, CNS infections, and metabolic/toxic etiologies are all potentially treatable
- RPD workup mnemonic — “VITAMINS”: Vascular, Infectious, Toxic-metabolic, Autoimmune, Metastatic/neoplastic, Iatrogenic, Neurodegenerative (prion), Systemic/seizures
- MRI DWI is the single most useful imaging sequence: cortical ribboning + caudate/putamen restriction in sCJD; mesial temporal FLAIR hyperintensity in autoimmune/limbic encephalitis
- Brain biopsy is the last resort: reserved for cases where extensive workup is nondiagnostic and a treatable condition remains possible
Definition & Approach
What Is a Rapidly Progressive Dementia?
- Timeframe: Onset to severe dementia in <1–2 years (many cases progress in weeks to months)
- Contrast with typical Alzheimer disease (AD): 8–12 year course from onset to severe dementia
- Key distinction: ~20–25% of RPDs have a potentially reversible cause — aggressive workup is mandatory
- Up to 60% of RPD cases ultimately are prion disease (sCJD); ~20% are neurodegenerative (rapidly progressive AD, DLB, FTD); ~20% are potentially treatable
VITAMINS Mnemonic for RPD Differential
| Letter | Category | Examples |
|---|---|---|
| V | Vascular | CNS vasculitis, intravascular lymphoma, cerebral amyloid angiopathy-related inflammation |
| I | Infectious | HIV/PML, Whipple disease, neurosyphilis, fungal meningitis |
| T | Toxic-metabolic | Bismuth, lithium, heavy metals, Wernicke encephalopathy, hepatic encephalopathy |
| A | Autoimmune | Anti-NMDAR, anti-LGI1, SREAT (Hashimoto), neurosarcoidosis, CNS lupus |
| M | Metastatic/Neoplastic | CNS lymphoma, intravascular lymphoma, leptomeningeal carcinomatosis, paraneoplastic |
| I | Iatrogenic | Immunosuppressants, chemotherapy (methotrexate), radiation, drug toxicity |
| N | Neurodegenerative | Prion disease (CJD), rapidly progressive AD, corticobasal syndrome, DLB |
| S | Systemic/Seizures | Nonconvulsive status epilepticus, thyroid disease, B12 deficiency, psychiatric (pseudodementia) |
💎 Board Pearl
- The VITAMINS mnemonic is the standard framework for RPD workup — boards often test the differential broadly to see if you consider treatable causes before defaulting to CJD
- Up to 10–25% of cases referred as “probable CJD” ultimately have an alternative (often treatable) diagnosis
Prion Diseases
Prion Biology
- PrPC (normal): Cellular prion protein — alpha-helix rich, GPI-anchored to cell membrane; physiologic function includes copper binding, cell signaling
- PrPSc (pathogenic): Misfolded isoform — beta-sheet rich; acts as a template to convert PrPC → PrPSc (self-propagating)
- No nucleic acid — prions are protein-only infectious agents (Nobel Prize: Stanley Prusiner, 1997)
- Resistant to: standard autoclaving, formalin, UV radiation, alcohol, boiling
- Decontamination requires: 1N NaOH or ≥20,000 ppm sodium hypochlorite for ≥1 hour; or autoclaving at 134°C for 18 minutes
- Neuropathology: Spongiform change (vacuolation), astrocytic gliosis, neuronal loss — no inflammatory infiltrate
Sporadic CJD (sCJD)
- Most common human prion disease (~85–90% of all CJD cases)
- Incidence: ~1–2 per million per year worldwide
- Mean age of onset: ~62 years (rare before 30 or after 80)
- Mean survival: ~5 months; 90% die within 1 year
Clinical Features
- Rapidly progressive dementia (100%)
- Myoclonus (90%) — startle-sensitive; most characteristic movement finding
- Akinetic mutism (late stage) — patient is awake but immobile and mute
- Cerebellar ataxia (70%) — may be presenting feature
- Visual/oculomotor abnormalities (40–50%) — cortical blindness (Heidenhain variant)
- Pyramidal and extrapyramidal signs
- Psychiatric symptoms (depression, anxiety, withdrawal) may precede cognitive decline
sCJD Subtypes by Codon 129 Polymorphism
| Subtype | Codon 129 | PrP Type | Clinical Features | Frequency |
|---|---|---|---|---|
| MM1/MV1 | Met/Met or Met/Val | Type 1 | Classic RPD + myoclonus; PSWCs on EEG; shortest duration | ~70% |
| VV2 | Val/Val | Type 2 | Prominent cerebellar ataxia at onset; dementia develops later | ~15% |
| MV2 | Met/Val | Type 2 | Longer course (up to 2 years); ataxia + dementia; kuru plaques | ~9% |
| MM2 | Met/Met | Type 2 | Cortical (slowly progressive dementia) or thalamic variant (insomnia) | ~4% |
Diagnostic Tests for sCJD
| Test | Sensitivity | Specificity | Key Points |
|---|---|---|---|
| MRI DWI/FLAIR | 92–96% | 93–97% | Cortical ribboning (restricted diffusion in cortex) + caudate/putamen signal; DWI > FLAIR sensitivity; most useful early diagnostic test |
| CSF RT-QuIC | 85–95% | 99–100% | Most specific antemortem test; detects PrPSc seeding activity; replaced 14-3-3 as preferred CSF test |
| CSF 14-3-3 protein | 85–95% | 40–70% | Nonspecific marker of rapid neuronal destruction; elevated in stroke, encephalitis, seizures — low specificity |
| CSF t-tau | 86–94% | 79–87% | Total tau >1,150 pg/mL supports diagnosis; more specific than 14-3-3; t-tau/p-tau ratio markedly elevated |
| EEG: PSWCs | 44–64% | 91–95% | Periodic sharp wave complexes (1–2 Hz); often absent early; more common in MM1 subtype; may appear late in disease |
| Brain biopsy/autopsy | ~100% | ~100% | Gold standard — spongiform change + PrPSc immunostaining; only definitive diagnosis; rarely needed clinically with RT-QuIC |
💎 Board Pearl
- RT-QuIC has replaced 14-3-3 as the preferred CSF test for CJD — near-perfect specificity (~99–100%) vs. poor specificity of 14-3-3
- DWI is more sensitive than FLAIR for early CJD detection — always order DWI sequences; cortical ribboning may be the earliest imaging finding
- PSWCs on EEG are late and subtype-dependent — present in ~64% of MM1 but may be absent in VV2 and MV2 subtypes; absence does not exclude CJD
- Codon 129 Met/Met homozygosity is the strongest genetic risk factor for sCJD and is associated with the most classic (and most common) presentation
CDC Diagnostic Criteria for sCJD
| Classification | Criteria |
|---|---|
| Definite | Neuropathologically confirmed (brain biopsy or autopsy) with PrPSc immunostaining or Western blot |
| Probable | Progressive dementia + ≥2 of: myoclonus, visual/cerebellar, pyramidal/extrapyramidal, akinetic mutism AND ≥1 of: PSWCs on EEG, positive CSF 14-3-3 with duration <2 years, high signal in caudate/putamen on MRI DWI/FLAIR, or positive RT-QuIC AND no alternative diagnosis |
| Possible | Progressive dementia <2 years + ≥2 of the clinical features above, but no supportive test results yet AND no alternative diagnosis |
Variant CJD (vCJD)
- Cause: Consumption of BSE (bovine spongiform encephalopathy/“mad cow disease”)-contaminated beef
- Age: Younger patients (median ~28 years) — contrast with sCJD (median ~62 years)
- Onset: Psychiatric symptoms (depression, anxiety, behavioral changes) — not cognitive decline
- Painful sensory symptoms (dysesthesias) in ~50% early in course
- MRI “pulvinar sign” — bilateral pulvinar high signal on FLAIR/T2; highly specific (~90%); “hockey stick sign” = pulvinar + dorsomedial thalamic signal
- EEG: PSWCs are absent (unlike sCJD)
- CSF 14-3-3: less reliably positive than in sCJD
- Tonsil biopsy: positive for PrPSc in vCJD (not in sCJD) — useful diagnostic test
- Duration: longer than sCJD (~13 months median)
- All confirmed vCJD cases to date: Met/Met homozygous at codon 129
- Neuropathology: “florid plaques” (PrP amyloid surrounded by spongiform change) — pathognomonic
💎 Board Pearl
- Pulvinar sign on MRI = vCJD (not sCJD) — bilateral high signal in the pulvinar nuclei of the thalamus; boards love this imaging finding
- Young patient + psychiatric onset + painful dysesthesias + pulvinar sign = vCJD
- sCJD = cortical ribboning + caudate/putamen; vCJD = pulvinar/thalamic signal — key MRI distinction
Genetic (Familial) Prion Diseases
- All caused by mutations in PRNP gene (chromosome 20); autosomal dominant
- Account for ~10–15% of all prion diseases
| Disease | Mutation | Key Features | Distinguishing Points |
|---|---|---|---|
| Familial CJD (fCJD) | E200K (most common), D178N-129V, V210I | Similar to sCJD but with family history; earlier onset | E200K most common worldwide; clusters in Libyan Jews, Slovakians, Chileans |
| Fatal Familial Insomnia (FFI) | D178N-129M | Intractable insomnia → dysautonomia → motor signs → dementia | Selective thalamic degeneration (anterior + dorsomedial nuclei); same D178N mutation as fCJD but linked to Met at codon 129 |
| Gerstmann-Sträussler-Scheinker (GSS) | P102L (most common), A117V, F198S | Cerebellar ataxia as predominant feature; dementia develops later; slower course (2–10 years) | Multicentric PrP plaques on pathology; younger onset; longer survival than CJD |
💎 Board Pearl
- D178N mutation = two different diseases depending on codon 129: D178N-129M → FFI (insomnia); D178N-129V → fCJD (dementia). Same mutation, different phenotype based on the cis polymorphism
- FFI = thalamus; GSS = cerebellum; fCJD = cortex — simplified anatomic localization of genetic prion diseases
- Intractable insomnia + dysautonomia + family history = FFI — think thalamic degeneration
Prion Disease Comparison Table
| Feature | sCJD | vCJD | fCJD | FFI | GSS |
|---|---|---|---|---|---|
| Frequency | 85–90% | <1% | ~10% | Rare | Rare |
| Age of onset | ~62 years | ~28 years | ~50 years | ~50 years | ~40–50 years |
| Duration | ~5 months | ~13 months | ~2 years | ~12–18 months | ~2–10 years |
| Presenting feature | Cognitive decline | Psychiatric/sensory | Cognitive decline | Insomnia | Cerebellar ataxia |
| Myoclonus | 90% | Uncommon early | Common | Late | Uncommon |
| EEG PSWCs | 64% (MM1) | Absent | Variable | Absent | Absent |
| MRI signature | Cortical ribboning + caudate/putamen | Pulvinar sign | Similar to sCJD | Thalamic atrophy (late) | Cerebellar atrophy |
| Pathology | Spongiform change | Florid plaques | Spongiform change | Thalamic gliosis | Multicentric PrP plaques |
Autoimmune Encephalitis as RPD
Overview
- Most important treatable RPD — early recognition and immunotherapy can reverse cognitive decline
- Can mimic CJD clinically and radiographically
- Always send serum AND CSF antibody panels in every RPD workup — some antibodies (e.g., NMDA-R) may be positive only in CSF
Key Antibodies Causing RPD
| Antibody | Target | Key Clinical Features | MRI Findings | Cancer Association |
|---|---|---|---|---|
| Anti-NMDAR | Cell-surface (NR1 subunit) | Psychiatric onset → seizures → movement disorder (orofacial dyskinesias) → autonomic instability → decreased consciousness | Often normal; may show mesial temporal or cortical FLAIR changes | Ovarian teratoma (20–50% in women) |
| Anti-LGI1 | Cell-surface | Limbic encephalitis; FBDS; hyponatremia (SIADH); older males | Mesial temporal T2/FLAIR hyperintensity | Rare (<5%) |
| Anti-CASPR2 | Cell-surface | Morvan syndrome: encephalopathy + neuromyotonia + insomnia + dysautonomia | Variable; may be normal | Thymoma (20–40%) |
| Anti-AMPAR | Cell-surface | Limbic encephalitis; memory loss; relapsing course | Mesial temporal FLAIR hyperintensity | SCLC, breast, thymoma (~70%) |
| Anti-GABA-B | Cell-surface | Limbic encephalitis; early refractory seizures; status epilepticus | Mesial temporal FLAIR hyperintensity | SCLC (~50%) |
| Anti-DPPX | Cell-surface | Prodromal GI symptoms (diarrhea, weight loss) → encephalopathy + hyperekplexia + myoclonus | Usually normal | Rare |
Clinical Pearl
- Autoimmune encephalitis can produce DWI cortical signal mimicking CJD — always consider autoimmune causes before concluding CJD; the key difference is that autoimmune encephalitis is treatable
- If CSF shows pleocytosis (WBC >5), this favors autoimmune/infectious over CJD (CJD CSF is typically acellular)
Paraneoplastic Causes of RPD
Intracellular (Onconeural) Antibodies
- Intracellular antibodies are biomarkers of T-cell-mediated neuronal destruction — antibodies themselves are not directly pathogenic
- Immunotherapy response is often limited because neuronal damage is irreversible; tumor treatment is primary therapy
- Strongly paraneoplastic — finding these antibodies mandates aggressive cancer screening
| Antibody | Associated Cancer | Clinical Syndrome | Key Points |
|---|---|---|---|
| Anti-Hu (ANNA-1) | SCLC (>80%) | Limbic encephalitis, sensory neuropathy, encephalomyelitis | Most common paraneoplastic antibody; poor prognosis |
| Anti-CV2/CRMP5 | SCLC, thymoma | Limbic/brainstem encephalitis, chorea, optic neuritis, peripheral neuropathy | Characteristic combination of CNS + PNS involvement |
| Anti-Ma2 (Ta) | Testicular germ cell (<50 years); lung cancer (>50 years) | Limbic/diencephalic encephalitis, narcolepsy-like symptoms, vertical gaze palsy | Young man + limbic encephalitis = check for testicular cancer |
| Anti-amphiphysin | Breast cancer, SCLC | Stiff-person syndrome, encephalomyelitis | May present with cognitive decline + rigidity |
💎 Board Pearl
- Cell-surface antibodies = potentially treatable; intracellular antibodies = search for and treat the tumor
- Young man with limbic encephalitis → anti-Ma2 → testicular ultrasound
- Anti-Hu + SCLC is the prototypical paraneoplastic limbic encephalitis — most common and most tested
- Negative initial cancer screen does NOT exclude paraneoplastic etiology — repeat imaging at 3–6 month intervals for ≥2 years
Other Causes of RPD
CNS Neoplastic/Infiltrative
- Primary CNS lymphoma: Can present as rapidly progressive cognitive decline; enhancing periventricular lesions; CSF cytology + flow cytometry; steroid-responsive (but biopsy before steroids)
- Intravascular lymphoma: “Great mimicker” — multifocal DWI lesions resembling vasculitis or CJD; random skin biopsy diagnostic; LDH markedly elevated
- Leptomeningeal carcinomatosis: Cranial neuropathies + radiculopathies + cognitive decline; enhancing meninges on MRI; CSF cytology (may need repeated LPs)
- Gliomatosis cerebri: Diffuse cerebral infiltration; progressive cognitive decline; diffuse T2/FLAIR abnormality on MRI
Inflammatory/Autoimmune (Non-antibody Mediated)
- Hashimoto encephalopathy (SREAT — Steroid-Responsive Encephalopathy Associated with Autoimmune Thyroiditis):
- Subacute encephalopathy + elevated anti-TPO or anti-thyroglobulin antibodies
- Thyroid function often normal or mildly abnormal
- Diagnosis of exclusion — antibodies are common in the general population; must exclude all other causes
- Key: dramatic response to corticosteroids
- CNS vasculitis (PACNS):
- Headache + cognitive decline + focal deficits; multifocal strokes
- MRI: multifocal white matter lesions, infarcts
- Conventional angiography: alternating stenosis/dilatation (“beading”); sensitivity only ~60%
- Brain + meningeal biopsy is the gold standard
- Neurosarcoidosis: Cranial neuropathies (especially facial nerve), hypothalamic dysfunction, leptomeningeal enhancement; elevated ACE (low sensitivity); biopsy: noncaseating granulomas
Infectious
- Whipple disease:
- Caused by Tropheryma whipplei
- Classic triad: dementia + oculomasticatory myorhythmia + GI symptoms (diarrhea, weight loss)
- Oculomasticatory myorhythmia = pathognomonic (convergent-divergent eye oscillations synchronous with jaw movements)
- Diagnosis: small bowel biopsy with PAS-positive macrophages; CSF PCR for T. whipplei
- Treatment: IV ceftriaxone × 2 weeks → TMP-SMX × 1 year; curable if treated
- HIV-associated dementia: Subcortical dementia pattern; CD4 typically <200; MRI shows diffuse white matter disease
- PML (Progressive Multifocal Leukoencephalopathy): JC virus in immunosuppressed; asymmetric white matter lesions without enhancement or mass effect; no effective antiviral — immune reconstitution is treatment
- Neurosyphilis: General paresis form → progressive dementia; check serum RPR/VDRL, CSF VDRL; treatable with IV penicillin
Rapidly Progressive Neurodegenerative Diseases
- Rapidly progressive AD: ~10% of AD cases may mimic RPD; can have myoclonus; MRI shows disproportionate atrophy; CSF AD biomarkers (low Aβ42, high p-tau/t-tau) help distinguish from CJD
- Dementia with Lewy bodies (DLB): May present subacutely; fluctuating cognition, visual hallucinations, parkinsonism, REM sleep behavior disorder
- Corticobasal syndrome: Asymmetric cortical + basal ganglia degeneration; alien limb, apraxia, cortical sensory loss
💎 Board Pearl
- Oculomasticatory myorhythmia is pathognomonic for CNS Whipple disease — if this is described in a vignette, the answer is Whipple regardless of other features
- SREAT is a diagnosis of exclusion — boards may present a patient with encephalopathy + anti-TPO antibodies, but you must exclude CJD, autoimmune encephalitis, and other causes first. The key confirmatory feature is dramatic steroid response
- Intravascular lymphoma mimics CJD on MRI with multifocal DWI restriction — random skin biopsy (even of normal-appearing skin) can make the diagnosis
RPD Workup Algorithm
Systematic Diagnostic Approach
| Phase | Tests | Rationale |
|---|---|---|
| Phase 1: Urgent (day 1–3) |
|
Rule out treatable emergencies (status epilepticus, infectious encephalitis, metabolic causes) |
| Phase 2: Targeted (day 3–7) |
|
Distinguish prion from autoimmune from paraneoplastic causes |
| Phase 3: Extended |
|
Cancer screening, genetic prion, rare infectious/toxic causes |
| Phase 4: Biopsy (last resort) | Brain + meningeal biopsy (nondominant frontal lobe) | When extensive workup nondiagnostic and treatable condition remains possible; diagnostic yield 57–65% |
Clinical Pearl
- Do not skip cancer screening in any RPD workup — intravascular lymphoma, leptomeningeal carcinomatosis, and paraneoplastic syndromes can all present identically to CJD
- Consider empiric immunotherapy (steroids + IVIg/PLEX) while awaiting antibody results if autoimmune etiology is suspected and the patient is deteriorating rapidly
Treatable vs. Untreatable RPD
Classification by Treatability
| Treatable / Potentially Reversible | Untreatable / Irreversible |
|---|---|
| Autoimmune encephalitis (anti-NMDAR, anti-LGI1, anti-CASPR2, anti-GABA-B, anti-AMPAR) | Sporadic CJD |
| Hashimoto encephalopathy (SREAT) | Variant CJD |
| CNS vasculitis (PACNS) | Familial CJD / FFI / GSS |
| Neurosarcoidosis | Rapidly progressive Alzheimer disease |
| CNS lymphoma | Rapidly progressive FTD |
| Intravascular lymphoma | Dementia with Lewy bodies |
| Whipple disease | Corticobasal degeneration |
| Neurosyphilis | Multiple system atrophy |
| HIV-associated dementia (with ART) | — |
| Nonconvulsive status epilepticus | — |
| Metabolic: B12 deficiency, thyroid disease, hepatic encephalopathy | — |
| Toxic: heavy metals, medication toxicity | — |
| Cerebral amyloid angiopathy-related inflammation | — |
💎 Board Pearl
- Boards love asking about reversible RPD — when a question asks “which of the following is potentially treatable,” autoimmune encephalitis, SREAT, Whipple disease, CNS vasculitis, and NCSE are the most commonly tested correct answers
- The entire purpose of an aggressive RPD workup is to find the ~20–25% of cases that are treatable — CJD is a diagnosis of exclusion only after treatable causes have been ruled out
- CSF pleocytosis argues AGAINST CJD and favors autoimmune or infectious etiologies — CJD CSF typically has normal cell counts
RPD Differential Diagnosis — Summary Table
| Diagnosis | Key Clinical Clue | Key Diagnostic Test | MRI Finding | Treatable? |
|---|---|---|---|---|
| sCJD | RPD + myoclonus + akinetic mutism | CSF RT-QuIC, 14-3-3, t-tau | DWI cortical ribboning + caudate/putamen | No |
| vCJD | Young + psychiatric onset + painful dysesthesias | Tonsil biopsy; MRI | Pulvinar sign (thalamic) | No |
| Anti-NMDAR encephalitis | Young woman + psychiatric + orofacial dyskinesias | CSF NMDA-R antibody | Often normal; mesial temporal FLAIR | Yes |
| Anti-LGI1 encephalitis | FBDS + hyponatremia + older male | Serum/CSF LGI1 antibody | Mesial temporal T2/FLAIR hyperintensity | Yes |
| Paraneoplastic (anti-Hu) | Smoker + limbic encephalitis + sensory neuropathy | Serum Hu antibody; CT chest | Mesial temporal FLAIR | Partially (tumor Rx) |
| SREAT | Encephalopathy + elevated anti-TPO + steroid-responsive | Anti-TPO; exclusion of other causes | Often normal; nonspecific white matter changes | Yes |
| CNS vasculitis | Headache + multifocal strokes + cognitive decline | Cerebral angiography; brain biopsy | Multifocal infarcts, white matter lesions | Yes |
| Whipple disease | Oculomasticatory myorhythmia + GI symptoms | Small bowel biopsy (PAS+); CSF PCR | Variable; may show brainstem/diencephalic lesions | Yes |
| Intravascular lymphoma | Multifocal DWI lesions + elevated LDH | Random skin biopsy | Multifocal DWI restriction mimicking CJD | Yes (chemo) |
| CNS lymphoma | Periventricular enhancing lesion + cognitive decline | CSF cytology/flow; stereotactic biopsy | Enhancing periventricular mass(es) | Yes (chemo/RT) |
| PML | Immunosuppressed + asymmetric white matter lesions | CSF JC virus PCR | Asymmetric subcortical white matter; no enhancement | Limited (immune reconstitution) |
| Rapidly progressive AD | Amnestic onset + myoclonus; CSF AD biomarkers | CSF Aβ42 low, p-tau/t-tau elevated | Disproportionate cortical/hippocampal atrophy | No |
| NCSE | Fluctuating encephalopathy; subtle motor signs | Continuous EEG monitoring | Often normal; may show cortical DWI changes | Yes |
Board Pearls & Clinical Pearls
💎 Board Pearl
- sCJD classic triad: rapidly progressive dementia + myoclonus + akinetic mutism — but cerebellar ataxia may be the presenting feature (VV2 subtype)
- RT-QuIC is the most specific antemortem test for CJD (~99–100% specificity) — has largely replaced 14-3-3 as the first-line CSF prion test
- DWI cortical ribboning + caudate/putamen = sCJD; pulvinar sign = vCJD — the single most important imaging distinction on boards
- EEG PSWCs are neither sensitive nor early — present in only ~64% of sCJD (mainly MM1 subtype); MRI DWI is more useful diagnostically
- CSF pleocytosis argues AGAINST CJD — if WBC >5 cells, reconsider autoimmune or infectious encephalitis
- Prions have no nucleic acid — protein-only infectious agents resistant to standard sterilization; requires NaOH or high-concentration bleach
- D178N-129M = FFI (insomnia); D178N-129V = fCJD (dementia) — same mutation, different disease based on cis codon 129 polymorphism
- Any RPD that is treatable and the patient improves is NOT CJD — CJD is invariably fatal with no effective treatment; improvement essentially rules it out
Clinical Pearl
- Do not anchor on CJD: Up to 10–25% of patients referred to prion surveillance centers as “probable CJD” have an alternative diagnosis, often treatable. Always complete the full RPD workup before concluding CJD.
- 14-3-3 protein is a marker of neuronal destruction, not CJD specifically — false positives occur with stroke, seizures, encephalitis, and CNS malignancy. RT-QuIC and MRI DWI provide far superior diagnostic specificity.
- Order RT-QuIC early in the workup — near-perfect specificity means a positive result essentially confirms prion disease, while a negative result should prompt more aggressive evaluation for treatable causes.
Clinical Pearl
- Empiric immunotherapy in RPD: If a patient is deteriorating rapidly and autoimmune encephalitis remains on the differential, it is reasonable to start empiric steroids + IVIg/PLEX while awaiting antibody results. A dramatic clinical response supports an autoimmune etiology and effectively rules out CJD.
References
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