A 55-year-old man with HIV comes to the emergency department due to 3 weeks of increasing headache, fever, and vomiting. Examination shows low blood pressure and neck stiffness. The patient's condition quickly deteriorates, and he dies in the hospital despite appropriate treatment. Autopsy of the brain shows a diffuse gelatinous exudate covering the base of the brain. Cut sections of the brain show marked ventriculomegaly and frontal lobe infarcts but no intraparenchymal mass lesions. Which of the following is the most likely diagnosis?
This patient's subacute symptoms and autopsy findings are highly suggestive of tuberculous (TB) meningitis, the most common central nervous system (CNS) manifestation of disseminated TB. TB meningitis arises when circulating bacilli lodge in the subependymal or subpial space, forming a tubercle that subsequently ruptures into the subarachnoid space. Common findings include the following:
A thick, gelatinous exudate most prominent in the basal portion of the brain. This exudate can encase the cranial nerves, leading to cranial nerve palsy, and invade the circle of Willis, leading to stroke.
Tuberculous vasculitis of the cerebral arteries. This can cause multiple bilateral brain infarctions, particularly in the periventricular cerebral areas.
Hydrocephalus due to obstruction of cerebrospinal fluid outflow by tubercular proteins. This can cause elevated intracranial pressure (eg, headache, nausea, vomiting) and ventriculomegaly.
Although CNS invasion occurs in only ~5% of extrapulmonary TB, risk is increased in those with significant immunocompromise due to HIV, immunosuppressive medications, advanced age, or malnutrition.
(Choice A) Herpes simplex virus type 1 can spread via the trigeminal nerve (CN V) to the brain. Patients usually develop rapid-onset (not subacute) fever, headache, seizure, altered mental status, and neurologic deficits. Autopsy typically shows unilateral temporal lobe inflammation, not hydrocephalus or a gelatinous exudate in the basal brain.
(Choice B) Neurocysticercosis is caused by the larval stage of the pork tapeworm Taenia solium. It is generally marked by intraparenchymal cysts at several stages of development. The lack of intraparenchymal lesions makes neurocysticercosis unlikely. In addition, patients generally present with seizures or focal neurologic deficits.
(Choice C) Primary CNS lymphoma is more common in patients with HIV but is usually marked by a single large mass in the parenchyma of the brain. The presence of a thick, gelatinous exudate and no intraparenchymal brain lesions would be atypical.
(Choice D) Toxoplasma encephalitis is common in patients with advanced HIV who are not on prophylaxis. Although it often presents with slowly progressive headache, vomiting, and/or fever, it is marked by multiple intraparenchymal lesions in the brain.
Educational objective:
Tuberculous (TB) meningitis is characterized by formation of a thick, gelatinous exudate in the base of the brain; cerebral vasculitis; and hydrocephalus. It frequently presents with subacute, slowly progressive nausea, vomiting, fever, cranial nerve deficits, and strokes.