Misdiagnosis of Dermatomyositis Save

JAMA Dermatology reports a retrospective cohort study from Johns Hopkins reviewing mimic of dermatomyositis (DM), suggesting that DM and especially clinically amyopathic DM (CADM) are commonly and initially misdiagnosed as inflammatory skin disease (ISD).

The study was undertaken to evaluate misdiagnosis patterns and the clinical implications of those with DM and CADM.

Study included adults with confirmed DM or CADM, seen between 2005 and 2023. Duration of misdiagnosis was defined as time between first ISD diagnosis and DM or CADM confirmation. 

A total of 260 patients (206 females [79%], age at diagnosis, 48.6 years) were studied, including 86 (33%) had CADM and 174 (67%) had DM.

• 125 patients with ISD, 73 (58%) received ISD diagnosis before DM or CADM diagnosis; 36 (29%) experienced misdiagnosis. 
  • Unspecified dermatitis and eczema were the most prevalent ISDs (22% and 19%). Cutaneous lupus erythematosus and eczema before DM or CADM diagnosis had the highest misdiagnosis rates (67% and 29%). 
• Among the misdiagnosis, 26 (72%) received their first skin evaluation by dermatology. 
• CADM cohort had higher misdiagnosis rates than DM cohort (44% vs 21%; P = .006)
• CADM had longer diagnostic delays (236 [67-332] vs 114 [35-263] days; P = .34)
• CADM group had higher DM-associated cancer rates (21% vs 11%; P = .03). 
• Misdiagnosed patients had higher 1-year hospitalization rates (54% vs 33%; P = .02) 
  • Misdiagnosis had lower DLCO values at ILD diagnosis (59% vs 86%; P = .01) and higher 1-year ILD incidence (71% vs 43%; P = .03) than those without misdiagnosis. 

DM, and especially CADM. was often misdiagnosed as other ISDs, with eczema (dermatitis & CLE) as notable mimics.

The consequences of a prolonged (mis)diagnosis were higher hospitalization, more ILD and worse DLCO at ILD diagnosis. 

Careful evaluation of atypical cutaneous features may lead to earliers and more accurate diagnoses of DM or CADM.