| Résumé : | Eosinophilic myositis constitutes a rare pathological entity characterized by eosinophilic infiltration of skeletal muscles, usually associated with parasite infections, systemic disorders, or the intake of drugs or L-tryptophan. The exclusion of such causes defines the spectrum of idiopathic EM. Based on a protein analysis performed in one affected patient, we recently identified CAPN3 mutations as a genetic cause of idiopathic eosinophilic myositis in a series of six paediatric patients. Here, we retrospectively included five additional patients diagnosed as being affected with idiopathic eosinophilic myositis. Whereas our previously reported cases of idiopathic eosinophilic myositis with CAPN3 mutations were only paediatric cases, we here describe one adult patient. Importantly, as in our previous series, the inclusion was based only on the particular histopathological presentation, in patients for whom no definitive aetiological diagnosis had been established. Disease-causing CAPN3 mutations were identified at a homozygous or compound heterozygous state in all patients, thus confirming the diagnosis of primary calpainopathy. Why eosinophilic infiltration can be correlated to defective calpain-3 needs to be further evaluated. Abnormal local interleukin secretion in calpain-3 deficient muscle tissue is one possibility. Also, T lymphocytes, which express the CAPN3 transcript, may be implicated in this process, as they are a main component of inflammatory lesions in the vicinity of damaged muscle fiber, and central in the chemotactism of eosinophils by secreting interleukin-5. In this regard, we recently identified one case initially diagnosed as lymphocytic myositis in which primary calpainopathy was diagnosed at the protein and genomic level. Altogether, the presence of marked eosinophilic infiltrates in patients affected with idiopathic eosinophilic myositis caused by CAPN3 mutations point to an important role of eosinophils in muscle damage caused by calpain-3 deficiency. |
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