Rapidly progressive dementia and Creutzfeldt-Jakob disease

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Rapid cognitive decline is a tempo-defined syndrome, not a synonym for prion disease. Build a week-by-week chronology of cognition, behaviour, sleep, seizures, movement, gait and independence. Fluctuation over hours with impaired attention suggests delirium; profound psychomotor slowing may mimic dementia in depression; subtle focal seizures or non-convulsive status can cause persistent confusion. Review immunosuppression, cancer, travel, infection, autoimmune symptoms, weight loss, alcohol, recreational exposure and every medicine, including lithium, anticholinergics and sedatives. Examine arousal, attention, language, memory, visual fields, eye movements, rigidity, bradykinesia, myoclonus, cerebellar signs, reflexes and startle. Routine blood tests and urgent structural imaging are the beginning, not the end, of the work-up.

Treatable categories must be actively pursued. Autoimmune encephalitis can cause psychiatric change, seizures, dyskinesia, autonomic instability and sleep disturbance; antibody-negative disease exists and immunotherapy decisions are specialist. Viral, bacterial, fungal and chronic infections depend on immune and exposure context. Metabolic causes include thyroid, hepatic, renal, calcium, sodium, B12 and thiamine disorders. Toxic causes, medication effects, subdural collections, multiple infarcts, dural fistula, vasculitis, lymphoma and leptomeningeal malignancy can progress quickly. MRI brain with contrast and diffusion, EEG and cerebrospinal-fluid cell count, protein, glucose, oligoclonal bands, microbiology, cytology and targeted antibody or prion studies are selected around phenotype and procedural safety. Empirical aciclovir or other treatment must not wait for complete testing when encephalitis is plausible.

CJD is a fatal transmissible spongiform encephalopathy with sporadic, genetic and acquired forms. Sporadic disease often progresses over months. MRI DWI and ADC abnormalities in cortex or striatum, positive CSF RT-QuIC and characteristic clinical findings can support a probable diagnosis without brain biopsy. Variant CJD has different epidemiology and often earlier psychiatric or sensory symptoms; acquired risk history should be explored through experts. Prions resist ordinary decontamination, but casual contact presents no transmission risk. The infection-control issue concerns instruments contacting high-infectivity tissues, neurosurgery, ophthalmic procedures and post-mortem practice. Follow current Advisory Committee on Dangerous Pathogens guidance and national service instructions; do not improvise or stigmatise routine care. Discuss diagnostic uncertainty honestly, identify a family contact, provide genetic counselling where indicated and involve palliative services early.

Key points

Rapidly progressive dementia evolves over weeks or months rather than years and is a diagnostic emergency because autoimmune, infectious, metabolic, toxic and neoplastic causes may be reversible.
First distinguish delirium, depression and non-convulsive status from a true progressive cognitive syndrome using attention, arousal, collateral timing and EEG where indicated.
Sporadic CJD commonly combines rapidly progressive cognitive decline with myoclonus, gait or limb ataxia, visual symptoms, pyramidal or extrapyramidal signs and later akinetic mutism.
MRI diffusion-weighted and ADC sequences may show cortical ribboning or caudate and putaminal diffusion restriction; the pattern must be reviewed by experienced neuroradiology.
CSF real-time quaking-induced conversion supports prion diagnosis with high specificity, while 14-3-3 and total tau reflect rapid neuronal injury and are less specific.
Periodic sharp-wave complexes on EEG can support sporadic CJD, but a normal or non-specific early EEG does not exclude disease and EEG is crucial for status epilepticus.
Autoimmune encephalitis, vasculitis, lymphoma, HIV or syphilis, Whipple disease, thyroid or B12 disease, drug toxicity and cancer-associated syndromes require history-led testing.
Contact the National Prion Clinic or National CJD Research and Surveillance Unit early rather than waiting for every result, and involve local infection prevention before biopsy or surgery.
There is no disease-modifying treatment for CJD; care prioritises clear communication, myoclonus and distress relief, nutrition, mobility, anticipatory planning and family support.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Prion disease

Sporadic CJD is most common, while inherited PRNP variants, acquired healthcare exposure and variant disease account for smaller clinically distinct groups.

Autoimmune and paraneoplastic disease

Neuronal-antibody encephalitis, vasculitis and cancer-associated immunity can cause rapidly progressive cognitive, movement and seizure syndromes that may be treatable.

Infection and inflammation

HIV, syphilis, Whipple disease, encephalitis and other infections can produce subacute cognitive decline with systemic or cerebrospinal-fluid clues.

Toxic, metabolic and structural disease

Medicines, organ failure, deficiency, non-convulsive seizures, lymphoma and vascular disease remain urgent alternatives to irreversible neurodegeneration.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Prion conformational conversion
Misfolded prion protein templates normal protein into the abnormal form, allowing self-propagating accumulation without nucleic acid.
2
Synaptic and spongiform injury
Protein accumulation disrupts synapses and causes vacuolation, gliosis and rapid neuronal loss across cortical, striatal and cerebellar networks.
3
Network collapse
Progressive tissue loss produces dementia, ataxia, visual symptoms, myoclonus, pyramidal or extrapyramidal signs and eventually akinetic mutism.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Prion phenotypeRed flag

Rapid cognitive decline with myoclonus, cerebellar or visual dysfunction and pyramidal or extrapyramidal signs is characteristic of sporadic CJD but not pathognomonic.

Autoimmune encephalitisRed flag

Subacute memory loss, psychiatric change, new seizures, faciobrachial or other abnormal movements, dysautonomia or hyponatraemia should prompt urgent specialist autoimmune assessment.

Non-convulsive statusRed flag

Fluctuating responsiveness, subtle twitching, gaze deviation or unexplained persistent confusion can represent ongoing seizure activity and requires urgent EEG-led treatment.

Toxic-metabolic patternRed flag

Medicine change, organ failure, electrolyte disturbance, malnutrition or exposure with diffuse neurological dysfunction can produce a rapidly reversible encephalopathy.

Cortical and striatal diffusionRed flag

Restricted diffusion involving cerebral cortex or caudate and putamen in the appropriate pattern raises prion concern, while hypoxia, seizures and metabolic disease are imaging mimics.

Akinetic mutism

Late loss of spontaneous movement and speech despite wakeful appearance can occur in advanced CJD and demands careful comfort, communication and family support.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Urgent MRI brain with DWI and ADCFirst step
Why
Identify prion-associated cortical or striatal restriction and structural, inflammatory, vascular or neoplastic alternatives.
Interpretation and limitations
Cortical ribboning supports CJD only in context; seizure, hypoxia and metabolic abnormalities can mimic it, so experienced neuroradiology review is important.
02
EEG
Why
Detect non-convulsive status and identify supportive periodic sharp-wave activity in a prion phenotype.
Interpretation and limitations
Periodic complexes are supportive but not universal, and non-specific slowing is common; an ictal pattern redirects management to urgent seizure treatment.
03
Lumbar puncture with targeted CSF studies
Why
Assess inflammation, infection, malignancy, autoimmune disease and prion biomarkers after imaging and safety review.
Interpretation and limitations
Pleocytosis argues against uncomplicated CJD and towards treatable inflammation or infection; RT-QuIC is more prion-specific than neuronal-injury proteins.
04
Blood metabolic, infectious and autoimmune screen
Why
Identify reversible systemic causes and guide more focused neuronal-antibody, vasculitic, cancer or infectious investigation.
Interpretation and limitations
Tailor testing to immune and exposure context; minor abnormalities should not terminate a broader work-up unless they plausibly explain the entire tempo and phenotype.
05
Body imaging and malignancy assessment
Why
Search for lymphoma, solid cancer or paraneoplastic trigger when systemic or autoimmune clues are present.
Interpretation and limitations
Select CT, PET or targeted imaging with specialists; a negative early cancer screen may need surveillance if a high-risk neuronal antibody is found.
06
Prion genetics and national review
Why
Classify possible inherited prion disease and obtain expert diagnostic synthesis and surveillance support.
Interpretation and limitations
PRNP testing requires consent and counselling because results affect relatives; national units guide sample handling and whether testing adds value.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Delirium

Fluctuating attention over hours or days from acute illness or medicines favours delirium, though it may coexist with an underlying progressive disorder.

Autoimmune encephalitis

Subacute psychiatric change, seizures, dysautonomia and inflammatory findings support a potentially reversible immune syndrome during assessment.

Non-convulsive status epilepticus

Persistent cognitive or behavioural change with subtle motor signs requires EEG because ongoing electrical seizure activity can mimic dementia.

Other neurodegenerative dementia

Alzheimer, Lewy-body and frontotemporal disorders usually progress more slowly, although aggressive variants and uncertain histories can overlap.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01First 24 hoursSearch first for reversible brain failureFirst stepCognition and function have deteriorated substantially over weeks or a few months.

1Stabilise physiology, assess attention and consciousness, review medicines and toxins, obtain collateral chronology and treat seizures, sepsis, hypoglycaemia or suspected encephalitis without avoidable delay.
2Perform detailed neurological examination and urgent blood, MRI and EEG assessment, selecting lumbar puncture after structural and procedural safety review.
3Send CSF for routine, infectious, inflammatory, cytological and antibody tests shaped by phenotype while preserving samples for specialist additions.
4Engage neurology early because empirical antimicrobial or immunotherapy decisions and rapidly changing airway or autonomic risk exceed routine outpatient assessment.

02Prion concernCoordinate expert diagnosis safelyClinical course and MRI, EEG or CSF findings raise possible CJD.

1Contact the National Prion Clinic or National CJD Research and Surveillance Unit for case review, RT-QuIC pathways, genetics and family communication support.
2Notify local infection prevention before neurosurgery, ophthalmic surgery, biopsy, endoscopy involving relevant tissue or post-mortem procedures, following current ACDP instrument guidance.
3Explain that ordinary social contact is safe and maintain dignified routine care, avoiding unnecessary isolation or delayed symptom treatment.
4Document the level of diagnostic certainty, outstanding mimics and a named family contact while national and local teams complete assessment.

03Progressive careAnticipate loss of movement and communicationA rapidly progressive disorder continues despite treatment or CJD becomes the leading diagnosis.

1Assess swallowing, nutrition, mobility, pressure risk, communication, myoclonus, anxiety, sleep and respiratory secretions with palliative and therapy teams.
2Use targeted symptomatic medicines at the lowest effective exposure, avoiding sedation that removes remaining interaction unless distress requires it.
3PreferredDiscuss preferred place of care, resuscitation, clinically assisted nutrition and future crises while the person can participate, using lawful best-interests processes later.
4Offer carers practical equipment, urgent contacts, bereavement preparation and genetic counselling when relevant to reduce abandonment during fast change.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

Treats a time-critical reversible mimic within the rapidly progressive cognitive syndrome while diagnostic testing continues.

Aciclovir for suspected viral encephalitis

Use the local emergency intravenous weight- and renal-adjusted regimen immediately when herpes encephalitis remains plausible; do not await all CSF results.

Ensure hydration and renal dose adjustment, monitor kidney function and intravenous access, and review continuation against PCR timing and specialist advice.

Can reduce disabling or frightening myoclonus in prion disease and other rapidly progressive neurological conditions.

Clonazepam for distressing myoclonus

Begin with a low specialist or palliative dose and titrate cautiously to comfort while preserving useful alertness where possible.

Sedation, falls, aspiration and respiratory depression matter; review concurrent opioids or sedatives and distinguish symptomatic relief from seizure management.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Akinetic mutism and death

Prion neurodegeneration advances to profound immobility, loss of communication, swallowing failure and death without disease-modifying treatment.

Aspiration and infection

Dysphagia, immobility and reduced consciousness cause pneumonia, pressure injury, thrombosis and malnutrition during advanced immobile disease.

Myoclonus and falls

Jerks, ataxia and visual dysfunction cause traumatic injury and make transfers increasingly unsafe during rapid decline.

Family and infection-control burden

Rapid decline creates severe psychological distress, while invasive procedures require specialist prion decontamination and tissue-handling precautions.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Repeat cognition, attention, consciousness, neurological signs and functional milestones frequently because diagnostic phenotype and airway risk can evolve over days.
Track seizures and myoclonus separately with EEG correlation where uncertain, avoiding automatic escalation of antiseizure therapy for every non-epileptic jerk.
Review swallowing, weight, hydration, aspiration, mobility, skin, continence and communication at each stage of rapid progression.
Maintain an outstanding-results list for CSF microbiology, antibodies, cytology, RT-QuIC, genetics and cancer screening with named clinical ownership.
Revisit infection-control plans before every invasive procedure, using current national guidance rather than adding broad restrictions to ordinary contact.
Assess family understanding, distress and practical capacity repeatedly; information delivered once may be impossible to absorb during a fast fatal illness.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Tempo is a laboratory result

Loss of independent function over six weeks demands a different investigation pathway from similar severity accumulated over six years.

Cortical ribboning has mimics

Diffusion restriction also follows seizures, hypoxia and metabolic injury; distribution, ADC behaviour and clinical course need expert synthesis.

RT-QuIC detects seeding

The assay amplifies abnormal prion-protein seeding activity and is more disease-specific than proteins released by rapid neuronal destruction.

Infection control is tissue specific

Prion precautions focus on high-infectivity tissue and instrument pathways; unnecessary isolation of normal care increases stigma without protecting staff.

A prion differential saves lives

Considering CJD should widen rather than close investigation because autoimmune encephalitis, infection, toxicity and seizures can closely imitate it and are treatable.

11Common pitfallsFrequent interpretation and management errors.

01
Calling rapid cognitive decline ordinary dementia and arranging a routine memory-clinic wait while a treatable encephalitis or seizure disorder progresses.
02
Diagnosing CJD from myoclonus alone or a radiology phrase without expert review of MRI pattern, CSF, EEG and alternative causes.
03
Using a negative early EEG or non-specific CSF neuronal-injury marker as definitive exclusion or confirmation of prion disease.
04
Delaying empirical aciclovir in a plausible encephalitis presentation while awaiting antibody or prion results.
05
Sending a patient for an invasive procedure without telling infection prevention that prion disease is suspected and checking instrument guidance.
06
Imposing unnecessary isolation or fear on relatives despite no risk from ordinary touching, feeding and social contact.