ANSWER 33
This woman has cerebral toxoplasmosissecondary to HIV infection. This condition is
caused by the protozoan Toxoplasma gondiiwhich primarily infects cats but can also be
carried by any warm blooded animal. In the West, 30–80 per cent of adults have been
infected by ingesting food or water contaminated by cat faeces, or by eating raw meat
from sheep or pigs which contain Toxoplasmacysts. After ingestion by humans the organ-
ism divides rapidly within macrophages and spreads to muscles and brain. The immune
system rapidly controls the infection, and the cysts remain dormant. The primary infec-
tion is generally asymptomatic, but can cause an acute mononucleosis-type illness with
generalized lympadenopathy and rash. It may leave scars in the choroid and retina and
small inflammatory lesions in the brain. If the host then becomes immunocompromised
the organism starts proliferating causing toxoplasmosis. This is an AIDS-defining illness,
but is relatively rare in solid organ transplant recipients. Cerebral toxoplasmosis usually
presents with a subacute illness comprising fever, headache, confusion, fits, cognitive dis-
turbance, focal neurological signs including hemiparesis, ataxia, cranial nerve lesions,
visual field defects and sensory loss. Movement disorders are common due to involvement
of the basal ganglia. CT or magnetic resonance imaging (MRI) will usually show multiple
bilateral ring-enhancing lesions predominantly located near the grey–white matter junc-
tion, basal ganglia, brainstem and cerebellum. The clinical and radiological differential
diagnoses include lymphoma, tuberculosis and secondary tumours. Anti-toxoplasma anti-
body titres should be measured, but are not always positive.
The other clues in this case to the diagnosis of HIV infection include the patient’s country of
origin, the weight loss and oral candidiasis. The headaches and papilloedema are caused by
raised intracranial pressure from the multiple space-occupying lesions. The hyponatraemia
is due to the syndrome of inappropriate antidiuretic hormone (ADH) secretion (SIADH) con-
sequent to the raised intracranial pressure.
This woman should be started on anticonvulsants to prevent further seizures. Treatment is
started with high-dose sulfadiazine and pyrimethamine together with folinic acid to pre-
vent myelosuppression. There should be a rapid clinical and radiological improvement. In
cases that have not responded within 3 weeks, a biopsy of one of the lesions should be
considered. Cerebral toxoplamosis is uniformally fatal if untreated, and even after treat-
ment neurological sequelae are common.
The patient should be counselled about HIV infection and consented for an HIV test. Her
HIV viral load and CD4 count should be measured, and antiretroviral drugs started. She
should be advised to contact her previous sexual partners so that they can be tested and
started on antiretroviral therapy. She should also tell her occupational health department
so that the appropriate advice can be taken about contacting, testing and reassuring
patients. The risk of HIV transmission from a healthcare worker to a patient is very small.
- Toxoplasmosis is the most common opportunistic infection of the central nervous system
in patients with AIDS. - Patients can present with headache, confusion, fits and focal neurological deficits.
- The clinical and radiological response to treatment is usually rapid.