Which condition is characterized by the presence of focal neurological deficits and a CD4 count less than 50?

The condition characterized by the presence of focal neurological deficits and a CD4 count less than 50 is progressive multifocal leukoencephalopathy (PML). PML is a rare but serious viral brain infection caused by the reactivation of the John Cunningham virus (JCV), which typically occurs in immunocompromised individuals, notably those with advanced human immunodeficiency virus (HIV) infection and a severely reduced CD4 T cell count.

In patients with a CD4 count less than 50, the risk of developing opportunistic infections increases significantly. PML presents with neurological symptoms that can vary based on the areas of the brain that are affected, leading to focal neurological deficits. These deficits may include weakness, sensory loss, cognitive impairment, or coordination problems, reflecting the demyelination of white matter in the brain caused by the viral infection.

While toxoplasmosis is another opportunistic infection seen in patients with low CD4 counts and can also present with focal neurological deficits, it typically causes lesions identifiable on imaging studies such as CT or MRI, whereas PML generally does not. Other conditions like pulmonary embolism and leptospirosis do not primarily present with these specific neurological deficits in the context of severely immunocompromised patients, making