Measles virus can lead years later to a chronic encephalitis characterized by behavioral changes and myoclonus; this condition is called ______.

• A. Guillain-Barré syndrome
• B. Subacute sclerosing panencephalitis
• C. Creutzfeldt-Jakob disease
• D. Multiple sclerosis

Answer: (B)

Subacute sclerosing panencephalitis is a chronic encephalitis caused by persistence of defective measles virus in brain tissue, usually appearing years after the initial infection. It presents with gradual behavioral changes and myoclonus as the disease slowly progresses, reflecting ongoing inflammation and demyelination in the CNS. This distinguishes it from Guillain-Barré syndrome, which affects the peripheral nerves and is typically acute after an infection; Creutzfeldt-Jakob disease, a prion disease with rapidly progressive dementia and myoclonus not linked to measles; and multiple sclerosis, an autoimmune CNS demyelinating disease not caused by persistent measles infection.