MRI of intracranial toxoplasmosis after bone marrow transplantation.

Toxoplasma encephalitis was confirmed by biopsy in three patients with bone marrow (BMT) or peripheral blood stem-cell transplantation (PBSCT). All had MRI before antimicrobial therapy. The intensity of contrast enhancement was very variable. One patient had one large, moderately enhancing cerebral lesion and several smaller almost nonenhancing lesions. The second had small nodular and haemorrhagic lesions without any enhancement. The third had late cerebral toxoplasmosis and showed multiple lesions with marked contrast enhancement. The moderate or absent contrast enhancement in the two patients in the early phase of cerebral toxoplasmosis may be related to a poor immunological response, with a low white blood cell count in at least one patient. Both received higher doses of prednisone than the patient with late infection, leading to a reduced inflammatory response. In patients with a low leukocyte count and/or high doses of immunosuppressive therapy, typical contrast enhancement may be absent.