Secondary seropositive result in a case of NAM: do not hesitate to repeat the tests

Necrotising autoimmune myopathy (or NAM) is a form of myositis without significant inflammation. Just recently reported, this condition is often considered to be related to the long-term oral use of statins. It involves a growing number of individuals of all ages, including children. The clinical picture is dominated by chronic myalgia, muscle deficit of varying significance, clearly elevated creatinine phosphokinase (CPK) level and presence of necrotic fibres combined with a positive result for Class I HLA labeling. In three-quarters of cases, one notes a positive result for specific autoantibodies such as the anti-SRP and anti-HMG-CoA reductase antibodies.

In an article published in June 2020, English rheumatologists reported the unprecedented observation of a female patient of mature age (69 years), who had had myalgia for six years, exposed several times to statins, and diagnosed as having NAM, even though the initial anti-SRP and anti-HMG-CoA reductase serologies were negative. Although she was treated successfully with a combination of corticosteroids and methotrexate for several years, she presented several clinical and laboratory relapses. During one of these relapses, six years after the NAM diagnosis was established, the anti-HMG-CoA reductase serology alone proved to be positive. This argument, confirming NAM, led the medical practitioners to proposing a rituximab treatment, which proved to be spectacularly effective after two treatment cycles. In the meantime, the positive status of the serology was confirmed using a different method in a second laboratory.


Initial seronegative immune-mediated necrotising myopathy with subsequent anti-HMGCR antibody development and response to rituximab: case report. Thomas R, Yeoh SA, Berkeley R, Woods A, Stevens M, Marino S, Radunovic A. BMC Rheumatol. 2020 Jun 30; 4:29.