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From the Journals

CADM Misdiagnosed Twice as Often as DM, Linked to Poorer Outcomes

Study reveals CADM patients face twice the misdiagnosis rate of DM patients, with diagnostic delays associated with increased hospitalization and ILD risks.

Conexiant

A retrospective cohort study conducted at Johns Hopkins Myositis Center found that nearly one-third of patients with dermatomyositis experienced misdiagnosis, with clinically amyopathic dermatomyositis patients facing higher rates of diagnostic errors and prolonged delays.

The study, published in JAMA Dermatology, evaluated 260 adults diagnosed with dermatomyositis (DM) or clinically amyopathic dermatomyositis (CADM) between 2005 and 2023 and examined patterns of misdiagnosis and associated clinical outcomes.

Among the cohort, 86 patients (33%) had CADM, while 174 (67%) had DM. Of 125 patients initially diagnosed with an inflammatory skin disease (ISD), 36 (29%) were ultimately misdiagnosed. CADM patients had significantly higher misdiagnosis rates than those with DM (44% compared with 21%, P = .006) and longer median diagnostic delays (236 compared with 114 days, P = .34).

The researchers found unspecified dermatitis (22%) and eczema (19%) were the most prevalent ISDs. Cutaneous lupus erythematosus and eczema before DM or CADM diagnosis had the highest misdiagnosis rates (67% and 29%, respectively). Among 27 misdiagnosed cases with skin biopsies, 24 (89%) demonstrated interface dermatitis, which proved critical in correcting many misdiagnoses.

Patients with a history of misdiagnosis had higher one-year hospitalization rates (54% compared with 33%, P = .02). While interstitial lung disease (ILD) prevalence was similar across groups, misdiagnosed patients had lower median diffusing capacity of the lungs for carbon monoxide (DLCO) at ILD diagnosis (59% compared with 86%, P = .01) and a higher one-year incidence of ILD (71% compared with 43%, P = .03).

Cancer outcomes were comparable between misdiagnosed and correctly diagnosed patients, though CADM patients had a higher overall incidence of DM-associated cancer (21% compared with 11%, P = .03).

The authors noted that study limitations included the single-center tertiary care design, which may not reflect broader misdiagnosis patterns, and reliance on electronic medical records data, which may introduce classification errors. They emphasized that careful clinical evaluation of atypical cutaneous features is associated with improved disease outcomes.

Full disclosures are detailed in the study.