Subacute Encephalopathies (Rapidly Progressive Dementias)

This is a group of conditions that are collected under the term subacute encephalopathy, which is also called rapidly progressive dementias. These conditions manifest with cognitive dysfunction over weeks or months. Therefore the onset and progression is slower than encephalopathy due to systemic disease and faster than usual causes of dementia which progress over years. The subacute encephalopthies encompass an uncommon group of conditions such as autoimmune or paraneoplastic limbic encephalitis, chronic meningitis, Creutzfeldt Jakob disease, Hashimoto’s encephalitis and central nervous system vasculitis. They require extensive investigations and significant clinical expertise to manage. It is important to think of these conditions in patients with encephalopathy who are not responding after treatment of systemic illness, and also in patients who present with this subacute time course.

Rapidly progressive dementia, investigations to consider:


  • Features of CJD, CNS vasculitis, paraneoplastic encephalopathy/encephalomyelitis

CT thorax, abdomen & pelvis:

  • Occult neoplasm

Blood tests:

  • Vasculitis screen: ESR, CRP, ANA screen, ENA panel (anti- dsDNA, anti-Sm, anti-RNP, SSA, SSB, anti-Jo-1, antitopoisomerase ‘formerly anti Scl-70’, antinucleolar, anticentromere), ANCA (c-ANCA, p-ANCA), Complement C3, C4 and CH50: SLE, Sjogren’s syndrome and others.
  • HIV, syphilis, Lyme serology
  • Mercury, lead, arsenic
  • Thiamine, vitamin B12 levels
  • Paraneoplastic antibodies/autoimmune antibodies: Anti-Hu (ANNA-1), CV2 (CRMP5), Ma2/Ta, amphiphysin, Yo, Ri, Zic4, voltage gated potassium channel (VGKC), anti-NMDA antibodies
  • Thyroid function tests TFTs & anti-thyroglobulin or anti-thyroperoxidase antibodies: Hashimoto’s encephalopathy

EEG: features of CJD, Hashimoto’s encephalopathy

  • Protein 14-3-3 & S100 protein: CJD
  • CMV PCR: CMV encephalitis in AIDS patients

Catheter angiogram: for CNS vasculitis
Tests for: CJD, Diffuse Lewy body disease, corticobasalganglionic degeneration,

Causes of subacute encephalopathy (rapidly progressive dementia):


Central nervous system vasculitis:

Chronic meningitis:

Prion disease:

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