Immune-mediated necrotizing myopathy: an emerging disorder.

Objectives: To describe the main features and the clinical management of a cohort of patients with immune-mediated necrotizing myopathy (IMNM).

Methods: We conducted an observational, monocentric, retrospective study of IMNM patients diagnosed in the Neuromuscular Unit of a tertiary hospital in Madrid (Spain) between 2013 and 2021.

Results: Sixteen IMNM cases were diagnosed, with a median age of 71.5 years (range 36-80), nine of whom (56.3%) were female. Thirteen (81.3%) patients had previously been treated with statins. The time from symptoms onset to diagnosis was less than six months in eleven (68.8%) patients and the most common clinical symptoms were proximal weakness and myalgia. The only myositis specific autoantibodies detected were anti-3-hydroxy-3-methyl-coenzyme A reductase in thirteen patients. The treatment strategy was based on prednisone, although a combination with other immunosuppressive drugs was required in eight (50%) patients.

Conclusions: There has been an increase in the diagnosis of immune-mediated necrotizing myopathies in the last few years. The anti-HMGCR antibodies were the only detected in this sample showing their key role in the diagnosis. Early recognition of the disease facilitate to start treatment as soon as possible, which should be based on the initial response to corticosteroids and usually requires a combination of several drugs.