A 30-year-old man is brought to the emergency department due to erratic behavior, progressive right-sided weakness, and difficulty walking for the last month. The patient was diagnosed with HIV several years ago and is not compliant with antiretroviral treatment. Physical examination shows a cachectic and disheveled man. Funduscopic examination shows no abnormalities. Motor strength in the right upper and lower extremities is decreased, and his gait is ataxic. Brain MRI reveals several discrete areas of demyelination in the subcortical and periventricular white matter with no surrounding edema or mass effect. CD4 cell count is 30/mm³. Reactivation of which of the following pathogens is most likely responsible for this patient's current symptoms?

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11ec160b_3852_4641_9249_27d0e0f34e99_MD0001_00 JC virus is a polyomavirus, typically acquired in childhood, that causes life-long, latent infection of the kidney and lymphoid organs. Most adults have serologic evidence of exposure but remain asymptomatic. However, those with severe immunosuppression, particularly patients with advanced AIDS, are at risk for viral reactivation with spread to the brain. The virus attacks oligodendrocytes, the cells that produce myelin, causing a severe demyelinating disease called progressive multifocal leukoencephalopathy (PML). PML typically presents with slowly worsening confusion, ataxia, motor deficits, and seizure. Brain MRI usually shows multifocal areas of white matter demyelination with no mass effect or enhancement. Diagnosis is confirmed with JC virus PCR testing of the cerebrospinal fluid; brain biopsy is rarely required. There is no specific treatment for PML, but patients with HIV who develop the disease are treated with antiretroviral therapy to reduce immune suppression. This often helps stabilize neurologic symptoms. (Choice A) Patients with advanced AIDS can occasionally develop cytomegalovirus encephalitis, which usually presents with rapidly progressive altered mental state and focal neurologic deficits. However, this condition is highly inflammatory so brain imaging typically shows enhancing lesions. (Choice B) Epstein-Barr virus reactivation can cause primary CNS lymphoma in patients with advanced AIDS. Patients usually have focal neurologic symptoms and altered mental state. However, brain MRI normally reveals a single enhancing lesion with mass effect. (Choice C) Herpes simplex virus encephalitis usually causes focal neurologic deficits and altered mental status. However, symptom onset is usually rapid (<1 week), most patients have fever, and brain imaging usually reveals an enhancing temporal lobe lesion with mass effect. (Choice E) Measles can cause subacute, sclerosing panencephalitis several years after initial infection. This fatal, progressive disease is characterized by slowly worsening neurologic symptoms and multifocal, enhancing, white matter lesions. (Choice F) Toxoplasma gondii is usually acquired by exposure to cat feces. Most patients are asymptomatic and have a life-long dormant infection. However, patients with advanced AIDS can have reactivation leading to meningoencephalitis (eg, headache, confusion, fever). Brain imaging usually shows several ring-enhancing lesions with surrounding edema. Educational objective: Patients with advanced AIDS can have reactivation of JC virus, which causes progressive multifocal leukoencephalopathy. This condition usually presents with slowly progressive confusion, ataxia, and motor deficits. Brain MRI reveals multifocal areas of white matter demyelination with no mass effect or enhancement.

A 30-Year-Old Man Is Brought to the Emergency Department Due