Severe rhabdomyolysis due to idiopathic inflammatory myopathies, a wary manifestation of a heterogenous pathology.

Idiopathic inflammatory myopathies (IIM) are historically classified by The Bohan and Peter criteria. The presentation of IIM is versatile and clinical-serological findings can aid in diagnosing the underlying form of IIM. Over the past years, the discovery and the use of myositis-specific autoantibodies (MSA) and myositis-associated autoantibodies (MAA) have led to a more heterogeneous classification by the European League Against Rheumatism and American College of Rheumatology (EULAR/ACR).This paper describes a case of dermatomyositis sine dermatitis. A 70-year -old woman presented with complaints of muscle weakness and was admitted because of severe oliguric renal failure due to rhabdomyolysis. Despite treatment with hemodialysis and initial recovery, her clinic worsened again. The disease course in combination with electromyography findings, PET-scan results, and positive myositis-specific autoantibodies, that is, anti-NXP-2 antibodies, ultimately led to the diagnosis.Today, commercial kits based on line immunoassay and dot blot have mostly replaced the labor-intensive immunoprecipitation of RNA and/or proteins for detecting MSA. Though it makes routine testing of multiple MSA easy to implement in clinical practice, more validation studies are required and clinicians should be aware of its limitations, including false-positive results. When clinical suspicion for IIM is high, a negative screening for antinuclear antibodies (ANA) result does not exclude IIM and the first test of choice remains a multi-specific immunoassay for the whole spectrum of MSA.In this paper, we want to underline that there is no shortcut in diagnosing IIM. Caution is required in interpreting different EMG, PET-scan, histological, and laboratory findings. Especially in the case of rhabdomyolysis, as this is a severe and wary manifestation of myositis.