ANCA-associated vasculitis after scrub typhus

Anti-neutrophilic cytoplasmic antibody (ANCA)-associated vasculitis is a primary systemic vasculitis that affects the small vessels, and ANCA is involved as the common pathogenesis. Environmental factors such as infectious agents have been considered to play a role in triggering the autoimmunity. We report here on a case of ANCA-associated vasculitis that developed after scrub typhus. A 64-year-old male was admitted because of fever, chills, pain, weakness and hypoesthesia of his calves. He was diagnosed as having scrub typhus based on the findings of an eschar and the positive serum anti-orientia antibody. The fever continued despite the antibiotic treatment. Neurologic symptoms such as numbness, hypoesthesia and weakness began to develop in the hands, feet and calves with a persisting fever. The nerve conduction velocity study revealed mononeuritis multiplex of the superficial peroneal nerve and the median nerve. Microscopic hematuria then additionally developed, and the serology showed a positive myeloperoxidase (MPO) test. A nerve biopsy was conducted on the left superficial peroneal nerve and the result showed non-infectious systemic vasculitis of the mediumsmall arteries. He was diagnosed as having microscopic polyangiitis along with ANCA associated vasculitis. The fever resolved and the neurologic symptoms began to improve after steroid pulse treatment (methylprednisolone 1 g/day). The neuropathy gradually improved after discharge. We presume that the ANCAassociated vasculitis was triggered by scrub typhus.