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Introduction Human T-lymphotropic virus 1 (HTLV-1) affects 5-10 million people worldwide. Neurologically, it most commonly manifests as a chronic myelitis but numerous neurological manifestations have been described.We describe a case series within our national HTLV-1 clinic identified to have an inflammatory myopathy.Methods We identified 7 patients with evidence of myopathy. We describe demographics, clinical phenotypes, investigations, histopathology and management strategies.Results We found middle-aged predominance, with median symptom onset at 66 years (range 24-69). Five patients were female and two male. Two patients had concomitant HTLV-1-associated myelopathy. All patients exhibited proximal weakness with lower limb predominance. One patient had an inclusion body myositis phenotype, three reported non-specific back pain, and two exhibited progressive dysphagia. All patients had an elevated creatine kinase (mean: 989 [336-1989]). Serum muscle autoantibodies were negative (performed in 4 patients). Muscle MRI (3 patients) demonstrated oedema and fatty infiltration affecting predominantly the anterior compartment of the thigh. Muscle biopsy (6 patients) demonstrated variable pathological findings, but all had inflammatory features. Patients were treated variably with pulsed corticosteroids, oral corticosteroids, methotrexate, ciclosporin and azathioprine. Whilst transient improvement was often noted with corticosteroids, patients continued to deteriorate on follow-up.Conclusion HTLV-1 infection can result in an inflammatory myositis, with or without HTLV-1-associated myelopathy. It may require treatment beyond the commonly associated myelopathy.michael.wride@nhs.net