A 42-year-old woman is brought to the office due to 2 weeks of personality changes. Her family reports that she has become withdrawn and does not talk as much as before. She has also had difficulty picking things up with her right hand. The patient has HIV infection and does not take her antiretroviral therapy consistently. She is a former smoker and used injection drugs in the past. The patient works in a food-processing facility and has not traveled recently. Temperature is 37 C (98.6 F), blood pressure is 126/78 mm Hg, pulse is 82/min, and respirations are 14/min. The patient is oriented to time, place, and person but is slow to respond to questions. Motor strength is decreased in her right upper extremity, with an exaggerated biceps reflex. CD4 count is 78 cells/mm3 and plasma HIV RNA is 400,000 copies/mL. CT scan of the head shows a small hypodense area in the left frontal lobe with ring enhancement after intravenous contrast administration. Two similar lesions are present in the basal ganglia and cerebellum. The infectious agent directly responsible for this patient's neurologic lesions is most likely transmitted by which of the following mechanisms?
Toxoplasma encephalitis | |
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TMP-SMX = trimethoprim-sulfamethoxazole. | |
This patient with undertreated AIDS has neurologic manifestations and multiple ring-enhancing brain lesions, raising strong suspicion for toxoplasmic encephalitis. The underlying pathogen is Toxoplasma gondii, an obligate intracellular parasite whose definitive host is cats. Transmission occurs when individuals come into contact with contaminated cat feces (eg, litter box or cat handling) and subsequently ingest oocytes or when patients ingest undercooked meat from an intermediate host (eg, pig, sheep).
Healthy individuals rapidly contain the infection via a cell mediated immune response and rarely develop clinical symptoms. However, latent infection is established (tissue cysts), and reactivation can occur in the setting of immunocompromise (eg, advanced AIDS). The most common manifestation of reactivation is toxoplasmic encephalitis, which is characterized by progressive headache, confusion, focal neurologic deficits, and/or seizure. Brain imaging classically shows multiple ring-enhancing lesions.
(Choice A) Mosquito bites can transmit viral pathogens (eg, West Nile, Zika) that can cause encephalitis. Patients may present with slowly worsening headache, confusion, seizure, or focal neurologic findings. However, viral pathogens do not typically cause ring-enhancing brain lesions.
(Choice B) Herpes virus type 1 is typically transmitted by close contact (eg, kissing) with an infected patient who has active lesions. Although this virus is the most common cause of sporadic encephalitis, imaging usually shows inflammation in the temporal lobe with edema and mass effect.
(Choice D) Cryptococcus neoformans, a fungus found in soil contaminated by bird (especially pigeon) droppings, is a common cause of meningoencephalitis in patients with untreated AIDS and usually presents with slowly worsening fever, malaise, and headache. However, ring enhancing lesions are not typically seen.
(Choice E) Bartonella henselae is a gram-negative bacterium transmitted to humans during a cat scratch. Healthy individuals can subsequently develop cat-scratch disease (regional lymphadenopathy), but patients with advanced AIDS are at risk for the more serious clinical syndrome of bacillary angiomatosis (violaceous, highly vascular skin lesions with constitutional symptoms). However, central nervous system manifestations are uncommon.
(Choice F) Syphilis can be transmitted by unprotected sexual intercourse, and patients with HIV are at greater risk for developing neurosyphilis. This often presents with confusion, meningeal symptoms (eg, stiff neck), eye abnormalities, and cranial nerve palsies. However, MRI of the brain usually shows leptomeningeal enhancement, not ring-enhancing lesions.
Educational objective:
Toxoplasma gondii is an intracellular parasite that is typically transmitted to humans after accidental ingestion of contaminated cat feces (eg, cat handling, litter box). Most initial cases are asymptomatic. However, the organism establishes a latent infection that can reactivate in the setting of severe immunocompromise, particularly advanced AIDS. Patients usually develop encephalitis with multiple ring-enhancing lesions.