G21.3 Postencephalitic parkinsonism

Name of the Condition

• Postencephalitic parkinsonism

Summary

Postencephalitic parkinsonism is a neurological condition characterized by parkinsonian symptoms (e.g., tremors, rigidity, bradykinesia) that develop following a viral encephalitis infection. It is a form of secondary parkinsonism resulting from damage to the brain, particularly the substantia nigra, caused by the infection.

Causes

This condition is caused by viral encephalitis, most notably the 1918–1926 epidemic of encephalitis lethargica (von Economo's encephalitis). The infection leads to inflammation and degeneration of brain structures involved in motor control, resulting in parkinsonian symptoms. Other viral or post-infectious processes may also contribute.

Risk Factors

• History of viral encephalitis, especially encephalitis lethargica.
• Severe or prolonged encephalitis infection.
• Age at the time of infection (older individuals may be more susceptible).
• Underlying neurological vulnerability.

Symptoms

• Resting tremors.
• Muscle rigidity.
• Bradykinesia (slowed movement).
• Postural instability.
• Masked facies (reduced facial expression).
• Speech and gait abnormalities.

Diagnosis

Diagnosis involves a detailed medical history focusing on prior encephalitis, a neurological examination to assess parkinsonian features, and exclusion of other causes of secondary parkinsonism. Imaging or lab tests may be used to rule out alternative diagnoses, but clinical correlation is key.

Treatment Options

• Symptomatic management with medications (e.g., levodopa) to address motor symptoms.
• Physical therapy to improve mobility and balance.
• Occupational therapy for daily function.
• Speech therapy for communication difficulties.
• Supportive care for associated symptoms (e.g., autonomic dysfunction).

Prognosis and Follow-Up

Prognosis varies; symptoms may stabilize or progress slowly. Long-term follow-up is essential to monitor motor function, manage complications, and adjust treatment. Regular neurological assessments help optimize care and address emerging issues.

Complications

• Progressive motor impairment.
• Falls and related injuries.
• Speech or swallowing difficulties.
• Mood disorders (e.g., depression, anxiety).
• Autonomic dysfunction (e.g., blood pressure fluctuations).

Lifestyle & Prevention

• Fall prevention strategies (e.g., home modifications).
• Regular exercise to maintain mobility.
• Balanced diet to support overall health.
• Avoidance of neurotoxins (e.g., pesticides) that may exacerbate symptoms.
• Vaccination against preventable viral infections (e.g., influenza) to reduce encephalitis risk.

When to Seek Professional Help

Seek immediate medical attention for sudden worsening of symptoms, severe tremors, difficulty breathing, or signs of infection (e.g., fever, confusion). Regular follow-up is recommended for symptom management and complication monitoring.

Tips for Medical Coders

Document the underlying encephalitis history and its temporal relationship to parkinsonian symptoms. Ensure clinical correlation between the infection and the onset of symptoms. Code G21.3 is specific to postencephalitic parkinsonism; avoid using it for other secondary parkinsonism causes.