A 42-year-old man with HIV infection who is nonadherent with antiretroviral therapy comes to the emergency department due to 3 weeks of increasing headache, vomiting, and lethargy. Temperature is 38.5 C (101.3 F), blood pressure is 130/80 mm Hg, pulse is 80/min, and respirations are 15/min. On examination, the patient is lethargic. Neck stiffness is present. Cardiopulmonary examination is normal. CT scan of the head shows moderate hydrocephalus and basilar meningeal enhancement; no mass lesions are present. CD4 count is 400/mm3. What is the most likely diagnosis?
Tuberculous meningitis | |
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Diagnosis |
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AFB = acid-fast bacillus; CSF = cerebrospinal fluid; NAAT = nucleic acid amplification test; TB = tuberculosis; WBC = white blood cell. | |
This patient's subacute fever, nuchal rigidity, and radiographic findings are highly suggestive of tuberculous (TB) meningitis. Meningitis occurs in approximately 5% of patients with extrapulmonary TB, but risk is increased in those with malnutrition, substance abuse, immunomodulatory medications, or HIV.
TB meningitis develops when bacilli spread through the bloodstream to the subpial or subependymal space. The organism forms nidi of infection (tubercles), which subsequently rupture into the subarachnoid space. It then triggers a significant hypersensitivity reaction, which results in the formation of a thick, gelatinous exudate that characteristically coats the basilar portion of the brain; this can usually be seen on imaging as basilar meningeal enhancement. Hydrocephalus frequently develops due to obstruction of cerebrospinal fluid outflow by tubercular proteins, and vasculitis can occur due to cerebral artery inflammation.
In contrast to other forms of bacterial meningitis, which typically cause severe symptoms within hours/days, TB meningitis usually presents with slowly progressive symptoms over weeks. Common manifestations include fever, vomiting, nuchal rigidity, headache, cranial nerve palsy, and stroke. Diagnosis is based on characteristic imaging findings and/or cerebrospinal fluid acid-fast bacilli stain, nucleic acid amplification testing, and culture.
(Choice A) Herpes encephalitis is marked by rapid-onset (not subacute) fever, headache, altered mental status, and/or seizure. Imaging typically shows unilateral temporal lobe enhancement, not hydrocephalus and basilar brain enhancement.
(Choice B) Neurocysticercosis is caused by the larval form of Taenia solium, a pork tapeworm. Patients typically have seizures or focal neurologic deficits, and imaging usually shows multiple intraparenchymal cysts at various stages of degradation.
(Choice C) Primary CNS lymphoma, an AIDS-defining illness, is generally marked by focal neurologic deficits or seizure; imaging typically shows a single ring-enhancing lesion in the brain.
(Choice D) Toxoplasma encephalitis is common in patients with AIDS who have CD4 counts <100/mm3. Although Toxoplasma encephalitis presents with subacute manifestations (eg, headache, fever, altered mental state), brain imaging will show multiple ring-enhancing lesions. This patient's CD4 count is 400/mm3, making Toxoplasma unlikely.
Educational objective:
Tuberculous meningitis is typically marked by subacute symptoms of meningeal irritation (eg, vomiting, headache, nuchal rigidity) and imaging findings of basilar meningeal enhancement, hydrocephalus, and stroke due to vasculitis. Risk is increased with immunocompromise (eg, HIV).