Comments on: Diagnostic classification of dermatomyositis with and without electrodiagnostic study: real-world clinical practice

Dear Sir, We have two comments on the recent article, ‘Diagnostic classification of dermatomyositis with and without electrodiagnostic study: real-world clinical practice’ by Pillai et al., describing their experience with 14 patients with dermatomyositis (DM) and evaluating the contribution of electrodiagnostic studies to the diagnosis.[1] First, the authors concluded that electromyography (EMG) can exclude the diagnosis of DM; however, this conclusion is not supported by the data. They had earlier stated that abnormalities are observed in 70%–90% of patients with inflammatory myositis and, in their study, not all patients with classical DM (CDM) and elevated creatine kinase (CK) had EMG findings suggestive of myopathy or myositis. Second, the authors proposed that all patients with suspected DM should undergo EMG. They identified two patients with CDM without characteristic cutaneous involvement who were excluded using the European League Against Rheumatism/American College of Rheumatology 2017 and the European Neuromuscular Centre 2018 criteria.[2,3] The EMG findings did not change the classification because, although both cases had weakness, high CK and positive specific antibodies, they lacked pathognomonic skin abnormalities. Incorporating mandatory needle examination would not have altered the classification in these cases, thereby undermining the argument that EMG would increase sensitivity to 100%. In patients who already satisfy the criteria for CDM, EMG would not provide additional diagnostic information. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.