Neurology · MU Sofia

45. Encephalitis and encephalomyelitis: classification, clinical features, examination methods, differential diagnosis

Covers encephalitis and encephalomyelitis, starting with definitions and then classifying them by cause (infectious, post-infectious or autoimmune, paraneoplastic) and by distribution (focal, diffuse, or involving brain and spinal cord). It goes on to pathogenesis, general and key clinical features, neurological examination with CSF findings, and differential diagnosis against meningitis, tumour, stroke, metabolic encephalopathy and abscess. It closes with a note on HSV encephalitis and its temporal lobe pattern.

Inside: 2 sections · 16 flashcards · 2 min

Topic 45 of 88 in the MU Sofia syllabus for Neurology (Medicine, Year 4). The free AceMed note covers it in 2 sections, about 315 words (2 min of reading), with 16 flashcards.

In this note

  1. Encephalitis and encephaolomyelitis - classificaiton, clinical features, examinaiton
  2. methods, differential diagnosis

methods, differential diagnosis

Definition

I.Encephalitis: Inflammation of the brain parenchyma (usually viral), causing altered consciousness + focal neurological signs + seizures.

II.Encephalomyelitis: Inflammation of brain + spinal cord (diffuse CNS involvement).

Classification

A. By Etiology

1. Infectious (most common): Viral (HSV-1 most important). VZV, enteroviruses, arboviruses. HIV (early/late CNS involvement)

2. Post-infectious / autoimmune: Acute disseminated encephalomyelitis (ADEM)

3. Paraneoplastic / autoimmune encephalitis: Anti-NMDA receptor encephalitis

B. By Distribution

  • Focal encephalitis (e.g., HSV → temporal lobe) localized to a specific area of the brain
  • Diffuse encephalitis widespread inflammation of the brain's parenchyma.
  • Encephalomyelitis (brain + spinal cord)

Pathogenesis

  • Viral invasion or immune-mediated injury
  • Neuronal damage + edema
  • Increased intracranial pressure
  • Possible hemorrhagic necrosis (HSV)

Clinical Features

A. General Symptoms: Fever. Headache. Malaise. Myalgia

B. Key Triad of Encephalitis: Altered mental status (confusion → coma). Seizures. Focal neurological deficits

C. Focal Signs: Aphasia. Hemiparesis. Cranial nerve deficits. Behavioral changes (limbic involvement)

D. Behavioral/Psychiatric Signs (important): Personality changes. Hallucinations. Memory impairment. (Especially in temporal lobe encephalitis)

E. Encephalomyelitis: Encephalitis symptoms + spinal cord signs. Weakness. Sensory level. Bladder dysfunction

Examination

General Examination: Fever. Toxic appearance. Neurological Examination

1. Mental status: Confusion. Disorientation. Reduced consciousness

2. Cranial nerves: Oculomotor abnormalities. Facial weakness. Dysphagia

3. Motor system: Hemiparesis. Hyperreflexia (UMN signs)

4. Sensory system: Variable deficits

5. Signs of meningeal irritation: May be present (meningoencephalitis)

6. CSF Findings (important): Mild ↑ opening pressure. Clear CSF. ↑ lymphocytes. Mild ↑ protein. Normal glucose (usually)

  • Exception: HSV encephalitis may show RBCs (hemorrhagic necrosis)

Differential Diagnosis

1. Meningitis: Prominent meningeal signs. No focal neurological deficits early. No major behavioral changes

2. Brain tumor: Gradual onset. Progressive focal deficits. No fever (usually)

3. Stroke: Sudden onset. No fever. No CSF inflammatory changes

4. Metabolic encephalopathy: No focal neurological signs. Normal imaging

5. Abscess: Focal signs + fever. Ring-enhancing lesion on imaging

Key Clinical Clues

  • HSV encephalitis (VERY IMPORTANT): Temporal lobe involvement.Aphasia. Memory loss. Behavioral changes. Seizures

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