Misdiagnosis is an important factor for diagnostic delay in McArdle disease.

Diagnosis of McArdle disease is frequently delayed by many years following the first presentation of symptoms to a health professional. The aim of this study was to investigate the importance of misdiagnosis in delaying diagnosis of McArdle disease. The frequency of misdiagnosis, duration of diagnostic delay, categories of misdiagnoses and inappropriate medical interventions were assessed in 50 genetically confirmed patients. The results demonstrated a high frequency of misdiagnosis (90%, n = 45/50) most commonly during childhood years (67%; n = 30/45) compared with teenage years and adulthood (teenage: n = 7/45; adult n = 5/45; not known n = 3/45). The correct diagnosis of McArdle disease was rarely made before adulthood (median age of diagnosis 33 years). Thirty-one patients (62%) reported having received more than one misdiagnosis; the most common were "growing pains" (40%, n = 20) and "laziness/being unfit" (46%, n = 23). A psychiatric/psychological misdiagnosis was significantly more common in females than males (females 6/20; males 1/30; p < 0.01). Of the 45 patients who were misdiagnosed, 21 (47%) received incorrect management. This study shows that most patients with McArdle disease received an incorrect explanation of their symptoms providing evidence that misdiagnosis plays an important part in delaying implementation of appropriate medical advice and management to this group of patients.