Résumé :
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In polymyositis, CD8 cells recognise unknown antigen linked to HLA. But in some cases, this antigen can be identified. A sixty years old Caribbean woman complained for progressive walking disability for ten years, without pain. In 2007, physical examination revealed a limb girdle weakness with Gower’s sign, thigh atrophy, but also left Babinski’s sign and brisk reflex, but no spasticity. CK were at 1400 U/l (N< 190). CT scan showed asymmetric atrophy of quadriceps. Encephalic and medullar MRI were normal. There was hyperproteinorachia (0.53g/l). Muscle biopsy was performed on left vastus medialis and microscopic features were consistent with polymyositis. Mononuclear cell infiltrate was surrounding and invading non necrotic fibers. Most of the lymphoid cells were immunostained by CD8 antibody. This finding supports a cytotoxic mechanism. Because the association of myositis with a slight myelopathy in a Caribbean woman, an HTLV1 serology was performed and was positive in serum and CSF. Tropical spastic palsy has a wide spectrum from pure spastic myelopathy to proximal myopathy with some pyramidal signs, which is observed in 9% to 25%. This case highlights the association of the HTLV1 virus and a possibly induced polymyositis. Both polymyositis and inclusion body myositis have had been described associated with HTLV1 virus infection even if remaining extremely rare. Furthermore, Retrovirus have been suspected to initiate an autoimmune pathway leading to an inflammatory response and sometimes to a chronic degenerative process. Chronic persistent viral infection might be an initiating factor in the genesis of inflammatory myopathies. Corticotherapy can improve the disease but there is often a lack of efficiency after few months. As HIV, HTLV1 virus can induce myositis and serology must be performed in Caribbean patients or spouses of Caribbean men with polymyositis.
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