Polymyositis: is there anything left? A retrospective diagnostic review from a tertiary myositis centre

Abstract

Objective The current classification criteria for idiopathic inflammatory myopathy (IIM) retain PM as a major disease subgroup. However, evolution in the understanding of IIM has suggested that many of these patients could be better described as having an alternative diagnosis. In the present study, we apply the latest understanding of IIM subtyping to retrospectively review PM diagnoses in a large cohort of IIM patients. Methods Within a previously reported cohort of 255 patients from a UK tertiary myositis clinic, 37 patients classified as PM according to both the EULAR/ACR IIM criteria and expert opinion were identified. Clinical data and complementary tests were reviewed, and consensus decisions regarding final classification were reached in each case. Results Nine (9/37, 24.3%) patients remained classified as PM, 3.5% (9/255) of the original cohort; these PM patients were seronegative for myositis antibodies, responsive to immunosuppression, and in 4/7 (57.1%) patients where muscle biopsy was performed had HLA-1 upregulation and endomysial inflammatory infiltrates. Immune-mediated necrotizing myopathy (5/37, 13.5%) and connective tissue disease overlap myositis (7/37, 19%) were the main alternative diagnoses. The remaining patients were diagnosed as: unspecified myopathy (6/37, 16%), dermatomyositis (2/37, 5%), cancer-associated myopathy (3/37, 8.1%), and non-inflammatory myopathy (1/37, 3%, myofibrillar myopathy). Four patients (4/37, 10%) had insufficient data available to confidently reclassify. Conclusion Our study confirms that PM can now be considered a rare IIM subgroup. A thorough examination, complete myositis autoantibody panel, and careful interpretation of the biopsy results is recommended to confirm the correct IIM sub-type.

A systematic review and meta-analysis to inform cancer screening guidelines in idiopathic inflammatory myopathies

“…Publication bias was observed with any ASS-related antibody, thus highlighting potential inaccuracy of calculated effect sizes. Recent advances in understanding raise the possibility that PM cases may actually represent other subtypes, such as IMNM or other neuromuscular disorders [ 94–96 ], thus potentially limiting the accuracy of the estimated cancer risk associated with PM. Calculation of the cancer risk associated with connective tissue disease-associated IIM (overlap IIM) was not possible due to varying classification.…”

Dysferlinopathy misdiagnosed with juvenile polymyositis in the pre-symptomatic stage of hyperCKemia: a case report and literature review

“…In a recent study of 255 patients classified as having definite or probable IIM by the current EULAR/ACR criteria [ 8 ], 124 were classified as PM, but only 37 (14.5%) were classified as PM according to expert opinion [ 9 ]. Furthermore, a detailed review of these 37 cases led to only 9 (24.3%) patients remaining classified as PM, corresponding only to 3.5% (9/255) of the original cohort [ 10 ].…”

Inclusion body myositis and associated diseases: an argument for shared immune pathologies

“…The diagnosis could be maintained in 9 patients (24.3%), while others were classified as other IIM entities based on serological and histopathological data. These 9 PM patients accounted for 3.5% of the total cohort of 255 IIM patients included in the analysis, indicating that PM might constitute a separate, but rare, subgroup of IIM [ 48 ]. Currently, PM remains a point of discussion with some authors arguing for a strict clinicopathological definition, while others advocate for a broader interpretation of PM, allowing for the inclusion of otherwise unclassifiable cases [ 45 ].…”