Subacute Sclerosing Panencephalitis: The Delayed Measles Complication: USMLE скачать в хорошем качестве

Subacute Sclerosing Panencephalitis: The Delayed Measles Complication: USMLE

Subacute Sclerosing Panencephalitis (SSPE) Overview Subacute sclerosing panencephalitis is a rare, fatal, and delayed complication of a measles infection. It typically manifests years after the initial infection, most frequently affecting children or adolescents. Clinical Presentation The classic clinical picture involves a child, often with an immigration history suggesting incomplete vaccination, presenting with progressive neurologic decline. • Initial Symptoms: Behavioral and cognitive decline, including personality changes, memory issues, and struggling in school. • Motor Dysfunction: Myoclonus (sudden jerky movements) is the hallmark sign, along with ataxia and spasticity. • Visual Deficits: Vision problems arise due to the involvement of the occipital cortex. • Late Stage: The disease leads to severe neurologic deterioration, including dementia, coma, and death within a few years. Pathophysiology The condition is caused by a mutated measles virus that persists within the brain. • Viral Characteristics: Measles is an enveloped, single-stranded RNA virus from the Paramyxoviridae family that produces hemagglutinin. This explains why brain biopsies in SSPE patients reveal an RNA virus containing hemagglutinin. • Mechanism of Persistence: The virus is never fully cleared after the primary infection. In SSPE, the virus often possesses a defective or absent matrix (M) protein. This defect prevents the virus from budding properly, causing it to remain trapped inside cells where it evades the immune system while continuing intracellular replication. • Neurological Damage: The persistent virus causes chronic inflammation, neuronal loss, and demyelination in neurons and glial cells. Risk Factors Children who immigrate from areas with low vaccination rates or limited access to routine immunization are at higher risk. These children are more likely to have experienced the wild-type measles infection necessary to develop SSPE later in life. Differential Diagnosis The combination of pediatric onset, cognitive decline, myoclonus, and viral features helps distinguish SSPE from other conditions: • Creutzfeldt-Jakob disease: Affects older adults and is caused by prions, not RNA viruses with hemagglutinin. • Guillain-Barré syndrome: An autoimmune demyelination of the peripheral nervous system presenting with ascending weakness, not cognitive decline or vision loss. • Multiple Sclerosis: Typically affects young adults with a relapsing-remitting course; biopsies show focal plaques rather than viral inclusions. • Progressive Multifocal Leukoencephalopathy (PML): Caused by the JC virus (a DNA virus) and occurs in immunocompromised patients. • Progressive Supranuclear Palsy: A tauopathy that affects older adults, causing parkinsonism and vertical gaze palsy. Key Memory Anchors • The "Classic" Patient: Child + cognitive decline + myoclonus + vision loss. • The Cause: Occurs years after measles infection. • The Lab Finding: RNA virus with hemagglutinin. • The Outcome: Fatal progressive encephalitis.