A study of muscle involvement in scrub typhus

• Muscle involvement occurs in 40% patients with scrub typhus.
• EMG and muscle histopathology findings are consistent with inflammatory myopathy.
• Muscle involvement in scrub typhus is transient and improves with treatment.

ObjectivesPatients with scrub typhus often complain of myalgia, but a comprehensive study on muscle dysfunction is lacking. We therefore report the clinical, electromyographic and muscle biopsy findings in patients with scrub typhus.MethodsConsecutive patients with scrub typhus were included, and their clinical and laboratory findings were noted. The patients with myalgia or weakness and elevated serum creatine kinase (CK) were considered to have muscle involvement. Electromyography (EMG) and muscle biopsy were done in some patients. Patients were treated with doxycycline 200 mg daily for 7 days, and their clinical and biochemical outcome on discharge and one month were evaluated.Results13 out of 33 (39.4%) patients had muscle involvement and their CK levels ranged between 287 and 3166 (859 ± 829) U/L. EMG revealed short duration polyphasic potentials, and muscle histopathology revealed evidence of vasculitis. There were significant correlations between severity of weakness and CK levels (r = − 0.6; p < 0.001), platelet counts (r = 0.4; p = 0.04), duration of illness (r = − 0.4; p = 0.01) and disability on discharge (r = − 0.4; p = 0.04). Patients with muscle involvement had more severe illness evidenced by a lower Glasgow Coma Scale score (p < 0.001), thrombocytopenia (p = 0.05) and greater disability on discharge (p = 0.007), when compared to those without muscle involvement. All the patients had complete recovery following doxycycline therapy, and CK levels also normalized.ConclusionMuscle dysfunction was present in 39% patients with scrub typhus. Although muscle histopathology showed evidence of vasculitis, patients responded to doxycycline.