Clinical Features

The incubation period of Balamuthia granulomatous amebic encephalitis (GAE) is unknown although, in disseminated infections with preceding cutaneous involvement, a few weeks to about 2 years may elapse between the appearance of skin lesions and the recognition of central nervous system (CNS) disease. Patients exposed through solid organ transplantation can develop symptoms of Balamuthia GAE more quickly, within a few days to weeks (range 12–24 days), possibly because of direct inoculation and immunosuppression. GAE symptoms can appear mild at first but can progress over weeks to months. Early symptoms might include mental health status abnormalities alone or in combination with fever, headache, stiff neck, nausea, vomiting, lethargy, ataxia, impaired speech, focal neurologic deficit, and seizures. Delayed diagnosis of Balamuthia GAE is not uncommon, as it may be easily confused with other neurologic diseases, even non-infectious ones, like stroke. The disease is usually fatal once it spreads to the brain.

Some patients with Balamuthia GAE have presented with rhinitis with sinus infections, otitis media, and/or skin lesions, often on the face (particularly involving the nose or cheek) but also on the torso or limbs. In patients with cutaneous involvement, most generally have a single lesion, but multiple lesions are also seen. These lesions are chronic and granulomatous in nature, beginning as papulonodular, erythematous, plate-like areas that enlarge over time. The lesions are typically painless but can ulcerate and cause tissue destruction. Involvement of the oral cavity, especially of the palate, may also be present. Most patients with Balamuthia skin lesions later develop GAE. However, many people with Balamuthia GAE (including most cases identified in the U.S.) never develop preceding skin lesions. In the published U.S. case series, only 8 patients had skin lesions.

Brain imaging is abnormal in Balamuthia GAE patients. Initially, magnetic resonance imaging (MRI) might show one or a few lesions, even when computed tomography (CT) scans of the brain are unremarkable. In the U.S. case series, typical findings included enhancing lesions, multifocal lesions, and edema. Lesions occurred in all parts of the brain. Over time, lesions can increase in size and number to involve the cerebral hemispheres, cerebellum, brainstem, and thalamus. Space-occupying masses and unifocal or multifocal ring-enhancing lesions up to 3–4 cm in diameter might be evident, and hydrocephalus and/or edema might also be present.