A rare case of ultrastructurally proven toxoplasmic myositis masquerading as necrotizing myopathy with emphasis on pathobiology.

Abstract

Toxoplasmosis is a zoonotic infection caused by the obligate protozoan Toxoplasma gondii. In an immunocompetent human host, the parasite forms bradyzoites (tissue cysts), mainly in skeletal muscle, eye, brain, or cardiac muscle, and remains latent. Once cysts are established, type 1 cytokine-based immunity controls the conversion to tachyzoites from bradyzoites. We propose that short-term immunosuppression can only cause a transient defect in this cycle of conversion control. The temporary lapse in conversion control releases few tachyzoites, and the host immunity in response gives rise to cytokines that can cause polymyositis. Myositis and the presence of a parasite in the muscle biopsy are very rare, even in immunosuppressed patients. We present a case of a young man with quadriplegia after immunosuppression for dengue-associated hemophagocytic lymphohistiocytosis. We report a rare case of toxoplasmic myositis in a patient masquerading as necrotizing myopathy, with emphasis on the possible pathomechanism of myositis and ultrastructure of toxoplasma. We recommend that toxoplasma myositis should be included among the differentials of sudden muscular weakness, especially in an immunocompromised host. Our case highlights the crucial role of muscle biopsy in the diagnosis of toxoplasmic myositis. For early diagnosis, a systematic search for toxoplasmosis should be formulated in case of polymyositis, especially in immunocompromised patients, as a quicker identification of the parasite is possible and treatment response is also better in the early, acute phase of toxoplasmic myositis.