Nervous system infections in patients with cancer.

The diagnostic approach to the patient with cancer with suspected CNS infection depends on an analysis of the patient's immune defect, the time course of development of manifestations of infection, and the type of clinical syndrome with supportive evidence for a specific diagnosis coming from laboratory and neuroradiographic data. Most patients with CNS infections can be grouped into those with signs of meningitis or meningoencephalitis and those with focal mass lesions. A smaller group presents with stroke-like onset. Except for the group with strokes, those with focal deficits usually present in a more indolent fashion, whereas those with meningitis and encephalitis present more acutely [63]. Patients with B-lymphocyte dysfunction are susceptible to encapsulated bacterial pathogens. Patients with T-lymphocyte impairment develop CNS infections that are caused by intracellular pathogens, particularly viruses (HSV, JC, CMV, HHV-6), Nocardia, Aspergillus, and Toxoplasma. Many noninfectious entities, such as drug treatment complications, radiation effects, recurrent tumor, and paraneoplastic syndromes, can mimic CNS infections. Although cryptococcosis, bacterial meningitis, and some viral infections are easily diagnosed from Gram's stain, culture, or PCR, patients with mass lesions may require tissue biopsy to confirm diagnosis. Patients with cancer differ from normal hosts in the distribution of pathogens, and there is a wider range of differential diagnostic issues, both infectious and noninfectious, for the relatively few clinical syndromes that present as potential CNS infections.