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