[Do neuromyosites exist?]

Neuromyositis defined as the association of dermatomyositis or polymyositis and a neuropathy without any found cause is a very controversial entity because of the possibility of, in one hand, muscular modifications caused by neurological involvement and, on the other hand, neurogenic type manifestations caused by polymyositis. The study of 4 cases seen in an Internal Medicine department and the review of the literature allowed us to show that the concept of neuromyositis corresponds to a clinico-pathological reality when the diagnosis is based on the association of definite criteria of both primary muscle and nerve involvement excluding muscular abnormalities that could be the consequence of nerve involvement and vice versa. The criteria, most relevant when associated are: a) for muscular involvement: high increase of muscular enzyme over 6 times the superior limit of the normal values, pseudomyotonic electrical discharges, perifascicular atrophy, intense inflammatory infiltrates and massive necrosis, b) for neurological involvement: early abolition of tendinous reflexes in a patient without notable muscular atrophy and with little or no myalgia, sensitive abnormalities in areas other than those of muscular involvement, especially when they are intense, early weakness of distal muscles, decrease of nerve conduction speed, target fibers and lesions of nerve trunks (and albuminocytological dissociation in the particular case of polyradiculoneuritis). Once the diagnosis of neuropathy settled, it is necessary to exclude an usual cause (alcoholism, diabetes...) before concluding to neuromyositis. When we apply these restrictive (but nevertheless necessary for the validity of diagnosis) criteria, only 6 cases of the literature respond to this entity. It is a peripheral neuropathy in 5 cases (like two of ours) and a polyradiculoneuritis in one case (like our two others). Among these 6 cases, there is a vasculitis in two, frequency much higher to what is observed in adult polymyositis, which suggest a possible causative role of vascular involvement in neuropathy arising. In the other cases we can just give pathogenic hypothesis making the neuropathy and the polymyositis the result of the same process (immunological disturbance, paraneoplastic origin, viral disease). In one of our four patients, who have shown an HTLV-I infection by polymerase chain reaction in situ hybridization was positive in muscle which suggest a direct pathogenic role of the virus. HTLV-I infection should be considered as a possible cause of neuromyositis especially in endemic areas.