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Difficulty: MediumInterpreting Imaging Results

A 4545-year-old man with a history of HIV infection presents to the emergency department due to a 44-week history of progressively worsening clumsiness of his right hand and difficulty walking. He admits to discontinuing his antiretroviral therapy two years ago. His vital signs are within normal limits. Neurological examination reveals right-sided hemiparesis, hyperreflexia in the right upper and lower extremities, and an unsteady, broad-based gait. His current CD4 +^+ lymphocyte count is 60 cells/mm360 \text{ cells/mm}^3. An MRI of the brain with and without gadolinium contrast is performed. The scan reveals several asymmetric, hyperintense lesions on T2-weighted and FLAIR sequences located in the subcortical white matter of the left frontal and parietal lobes. The lesions do not demonstrate contrast enhancement, and there is no evidence of perilesional edema or mass effect.

Which of the following is the most likely diagnosis based on these imaging findings?

  1. A
    Cerebral toxoplasmosis
  2. B
    Cytomegalovirus encephalitis
  3. Progressive multifocal leukoencephalopathyAnswer
  4. D
    HIV-associated neurocognitive disorder
  5. E
    Primary central nervous system lymphoma

Answer

Progressive multifocal leukoencephalopathy
Progressive multifocal leukoencephalopathy (PML) is a central nervous system demyelinating disease caused by the JC virus, predominantly affecting severely immunocompromised patients. The characteristic MRI findings are multiple, asymmetric, focal hyperintense lesions on T2-weighted and FLAIR imaging located in the subcortical white matter. Crucially, these lesions do not typically demonstrate contrast enhancement, nor do they produce significant perilesional edema or mass effect. These specific imaging characteristics accurately match the findings described in the patient, confirming the diagnosis.

Step-by-Step Solution

1
Evaluate the patient's immune status and symptom onset.
The patient has advanced, untreated HIV with a low CD4 count and subacute, asymmetric focal neurologic deficits.
Establishing the clinical context and time course helps narrow the differential for opportunistic CNS infections.
2
Analyze the specific findings on the brain MRI.
The MRI shows asymmetric, T2/FLAIR hyperintense subcortical white matter lesions lacking contrast enhancement, mass effect, or perilesional edema.
Accurate interpretation of the presence or absence of enhancement and mass effect is the critical differentiating factor among CNS lesions in immunocompromised states.
3
Correlate imaging features with the differential diagnosis.
The imaging findings specifically match Progressive multifocal leukoencephalopathy, ruling out conditions with typical enhancement or edema like toxoplasmosis and lymphoma.
Finalizing the diagnosis requires matching the distinct radiographic pattern to the correct pathophysiology.

Key Concept

Interpreting characteristic MRI findings of Progressive Multifocal Leukoencephalopathy (PML) to differentiate it from other central nervous system lesions in immunocompromised patients.
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Topics

Interpreting Imaging Results

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