Encephalitis of the basal ganglia in an injection drug user.

Figure 2. Gadolinium-enhanced MRI sequence showing ring-enhancing lesions within the basal ganglia (arrow). Figure 1. Fluid-attenuated inversion recovery MRI sequence demonstrating vasogenic and cytotoxic edema in the bilateral basal ganglia (arrows). Diagnosis: Isolated cerebral mucormycosis of the basal ganglia. Brain biopsy tissue was obtained by stereotactic biopsy of the right basal ganglia ring-enhancing lesion (figures 1 and 2). Microscopic examination of samples stained with hematoxylin and eosin (figure 3) and Grocott methenamine silver (figure 4) revealed pauciseptate irregularly branching fungal hyphae, associated with granulomatous inflammation and acute hemorrhage. The hyphae were morphologically consistent with members of the division Zygomycota and order Mucorales. Fungal culture of the specimen grew Pseudomonas, Penicillium, and Alternaria species, whereas bacterial cultures remained sterile , indicating gross contamination of the fungal culture. Therefore , ribosomal DNA was amplified by PCR from paraffin-embedded tissue using broad host-range fungal-specific primers [1, 2]. The amplified products were cloned and sequenced. When compared using BLAST with sequences available in GenBank, the closest match (190% sequence match) was to Rhizopus arrhizus. Zygomycetes are ubiquitous saprophytic organisms [3]. Classically , CNS zygomycosis has been reported in patients with diabetic ketoacidosis and other immunocompromised states as a result of direct extension of sinus disease into the orbit, eye, optic nerve, and brain parenchyma, including the frontal and temporal lobes [3–5]. Zygomycosis may also present as cav-ernous sinus thrombosis (11%) or, more rarely, as isolated ischemic infarction caused by internal carotid or basilar arteritis [4, 6]. Zygomycetes are angioinvasive, producing tissue necrosis in addition to inflammation, and patients may also present with hemorrhagic infarction secondary to formation and rupture of a mycotic aneurysm [3]. Figure 3. Brain biopsy specimen stained with hematoxylin and eosin (original magnification, ϫ120) showing pauciseptate fungal hyphae (arrows) with surrounding granulomatous inflammation and hemorrhage. Figure 4. Brain biopsy stained with Grocott methenamine silver (original magnification, ϫ180) demonstrating irregularly branching fungal hy-phae (arrow). Approximately 30 cases of isolated cerebral zygomycosis in immunocompetent individuals have been reported, and most of these patients have been injection drug users [7–12]. In contrast with the presentation in immunocompromised patients , zygomycetes show a remarkable predilection for the basal ganglia and thalamus in immunocompetent patients [3, 7, 9– 16]. These lesions are typically unilateral, although bilateral involvement has been reported [10, 15]. Other CNS sites affected include the corpus callosum, frontal lobes, and brainstem [10, 11, 14]. Exposure is thought to be secondary to inoculation with …