High prevalence of paraspinal muscle involvement in adults with McArdle disease

Introduction/Aims Very few studies analyzing the pattern of muscle involvement in magnetic resonance imaging (MRI) of patients with McArdle disease have been reported to date. We aimed to examine the pattern of muscle fat replacement in patients with McArdle disease. Methods We performed a retrospective study including all patients with genetically confirmed McArdle disease followed in our center from January 2010 to March 2021. Clinical data were collected from the medical record. Whole-body MRI was performed as part of the diagnostic evaluation. The distribution of muscle fat replacement and its severity were analyzed. Results Nine patients were included. Median age at onset was 7 y (range, 5-58) and median age at the time when MRI was performed was 57.3 y (range, 37.2-72.8). At physical examination, four patients had permanent weakness: in three the weakness was limited to paraspinal muscles, whereas in one the weakness involved the paraspinal and proximal upper limb muscles. Muscle MRI showed abnormalities in six of the seven studied patients. In all of them, fat replacement of paravertebral muscles was found. Other muscles frequently affected were the tongue in three, subscapularis in three, and long head of biceps femoris and semimembranosus in two. Discussion Our findings suggest that paraspinal muscle involvement is common in McArdle disease and support the need to include this disease in the differential diagnosis of the causes of paraspinal muscle weakness. Involvement of the tongue and subscapularis are also frequent in McArdle disease.