Intracerebral mass lesions in patients affected by AIDS

Intracranial Toxoplasma gondii granuloma in a cat

An 8-year-old cat with recent-onset generalized seizures was diagnosed with a right forebrain mass using magnetic resonance imaging. The mass was excised and upon histologic and immunohistochemical examination shown to be a Toxoplasma gondii granuloma. Serology supported active T gondii infection. The cat was treated with phenobarbital to control seizures. After definitive diagnosis of toxoplasma granuloma, clindamycin was administered for approximately 1 month. Seizures recurred 8 months after initial presentation, and the cat was euthanased at the owner's request. This is a previously unreported manifestation of feline central nervous system toxoplasmosis. When a mass lesion is present in the brain of a cat and serologic test results support active infection with T gondii, toxoplasma granuloma must be a differential diagnosis. If the patient is suffering from clinical disease, surgical resection of the mass (if possible) can be complimented with medical treatment until definitive diagnosis is obtained. Immunocompromising factors should be identified and addressed if possible.

Inhibition and structure of Toxoplasma gondii purine nucleoside phosphorylase

The intracellular pathogen Toxoplasma gondii is a purine auxotroph that relies on purine salvage for proliferation. We have optimized T. gondii purine nucleoside phosphorylase (TgPNP) stability and crystallized TgPNP with phosphate and immucillin-H, a transition-state analogue that has high affinity for the enzyme. Immucillin-H bound to TgPNP with a dissociation constant of 370 pM, the highest affinity of 11 immucillins selected to probe the catalytic site. The specificity for transition-state analogues indicated an early dissociative transition state for TgPNP. Compared to Plasmodium falciparum PNP, large substituents surrounding the 5'-hydroxyl group of inhibitors demonstrate reduced capacity for TgPNP inhibition. Catalytic discrimination against large 5' groups is consistent with the inability of TgPNP to catalyze the phosphorolysis of 5'-methylthioinosine to hypoxanthine. In contrast to mammalian PNP, the 2'-hydroxyl group is crucial for inhibitor binding in the catalytic site of TgPNP. This first crystal structure of TgPNP describes the basis for discrimination against 5'-methylthioinosine and similarly 5'-hydroxy-substituted immucillins; structural differences reflect the unique adaptations of purine salvage pathways of Apicomplexa.

Cranial computed tomography in the emergency department evaluation of HIV-infected patients with neurologic complaints

STUDY OBJECTIVE

To demonstrate the usefulness of cranial computed tomography (CT) in the emergency department evaluation of HIV-infected patients and patients with risk factors for HIV infection who present with neurologic complaints.

DESIGN

Retrospective review of imaging reports and medical records of patients who visited the ED from March 1991 through March 1992.

SETTING

Urban university ED.

PARTICIPANTS

Patients with HIV infection or risk factors for infection who underwent emergency cranial CT after presenting to the ED with headache, altered mental status, focal deficits, or other neurologic signs or symptoms.

RESULTS

One hundred forty-six patients visited the ED 169 times. Of the 169 cranial CTs obtained, 85 (50%) were normal, 49 (29%) showed atrophy only, and 35 (21%) demonstrated focal lesions, with mass effect noted in ten (6%). Enhancing lesions were present in 13 scans. In 21 (12%) cases, CT revealed either an indication for admission, a contraindication to lumbar puncture, or both. In 25 instances, patients with lesions had nonfocal presentations and no papilledema. Two presentations--focal deficit and altered mental status--were each statistically significantly associated with lesions on CT. In seven patients with multiple ED visits, repeat CT showed new findings. Among patients who had risk factors but were of unknown HIV status, there was the same proportion of abnormal scans as in known HIV-infected patients.

CONCLUSION

CT detected clinically significant neuropathology among our study patients. Because lesions and mass effect were associated with nonfocal as well as focal presentations, CT is indicated in every neurologically symptomatic patient with HIV infection or risk factors for infection. Because HIV-related diseases can progress rapidly, repeat CT is recommended even in patients with recent scans.