A 43-year-old man is brought to the emergency department due to confusion and left-sided weakness. He has been living in a homeless shelter for the past month, and a staff member says that the patient has had progressive memory impairment, difficulty communicating, and left-sided weakness. The patient was diagnosed with HIV infection 4 years ago and had an episode of Pneumocystis pneumonia 6 months ago. He has not been compliant with antiretroviral therapy. Temperature is 37.1 C (98.8 F), blood pressure is 130/80 mm Hg, pulse is 78/min, and respirations are 16/min. Physical examination shows a disheveled and cachectic man with oral thrush. The patient is not oriented to time, place, or person and has expressive aphasia. Left-sided hyperreflexia, hypertonia, and upgoing plantar reflex are present. CD4 count is 30/mm³, and toxoplasma serology is positive. CT scan of the brain with intravenous contrast reveals several asymmetric, hypodense, nonenhancing white matter lesions with no edema. Which of the following is the most likely cause of this patient's current condition?

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11ec25c8_d141_a5a8_bc81_1192dce60522_MD0003_00 This patient with untreated AIDS has progressive neurologic symptoms and imaging evidence of nonenhancing, asymmetric white matter lesions, raising strong suspicion for progressive, multifocal leukoencephalopathy (PML), a life-threatening neurologic disease caused by the reactivation of JC virus. JC virus is usually acquired in childhood and lies dormant in the kidneys and lymphoid tissue; most individuals remain asymptomatic. However, those with severe immunocompromise (eg, AIDS with CD4 count <200/mm³) are at risk for reactivation. Reactivated virus spreads to the CNS and lyses oligodendrocytes, causing white matter demyelination. Symptoms include altered mental status, motor deficits, ataxia, and vision abnormalities (eg, diplopia). CT of the brain with contrast usually reveals asymmetric, nonenhancing, hypodense white matter lesions with no surrounding edema. Diagnosis requires lumbar puncture with cerebral spinal fluid evidence of JC virus (by polymerase chain reaction). Brain biopsy is rarely required. There is no specific treatment for PML, but initiation of antiretroviral therapy (in patients with AIDS) can sometimes prevent progression and death. However, most patients have long-term neurologic sequalae. (Choice A) Cerebral toxoplasmosis is the most common CNS infection in patients with untreated AIDS and often causes headache, confusion, fever, and focal deficits. However, imaging typically reveals multiple ring-enhancing lesions with edema (not nonenhancing lesions with no edema). Although this patient's positive toxoplasma serology indicates previous exposure (which is quite common), it does not indicate reactivated/active disease. (Choice B) Herpes simplex encephalitis usually causes acute (not subacute) fever, headache, seizures, focal deficits, and altered mental status. Imaging typically reveals unilateral temporal lobe-enhancing lesions with mass effect. (Choice C) HIV-associated dementia can cause behavioral and personality changes in those not on ART. However, MRI brain usually shows diffuse brain atrophy, ventricular enlargement, and reduced attenuation of white matter structures. The presence of focal, asymmetric white matter lesions in this case make HIV-associated dementia much less likely. (Choice D) Kaposi sarcoma usually causes cutaneous lesions, sometimes with gastrointestinal or mucous membrane involvement. Brain lesions are extremely rare. (Choice E) Multiple sclerosis (MS) is also an inflammatory, demyelinating CNS disease; however, imaging usually reveals well-circumscribed (not irregular) white matter lesions. In addition, MS flares are uncommon in patients with advanced AIDS. (Choice F) Although primary CNS lymphoma is an AIDS-defining illness that occurs much more often in patients with advanced AIDS (compared to the general population), imaging usually reveals a single, well-defined, ring-enhancing lesion with surrounding edema. The presence of multiple asymmetric lesions and lack of enhancement/edema makes primary CNS lymphoma unlikely. (Choice H) Subacute sclerosing panencephalitis is a progressive, fatal disease that occurs years after measles infection. Imaging reveals brain scarring and atrophy. Educational objective: Progressive multifocal leukoencephalopathy is caused by JC virus reactivation and occurs primarily in patients with advanced HIV (CD4 count <200/mm³). Manifestations include subacute neurologic changes (eg, mental status change, motor deficits, ataxia) and imaging evidence of multiple nonenhancing brain lesions with no mass effect (edema).

A 43-Year-Old Man Is Brought to the Emergency Department Due