FRI0410 Adult pompe’s disease: screening in patients with myopathies of unknown etiology

Background Pompe´s disease is an inherited metabolic myopathy caused by deficiency of the lysosomal enzyme acid α-glucosidase. In adults, it may be misdiagnosed as other chronic muscle disease such as limb girdle muscular dystrophy or polymyositis (PM), among others. Until now diagnosis was difficult and substitutive treatment not available, but recently the development of enzymatic methods using dried blood spots (DBS) on filter paper as a simple, quick and inexpensive first test, as well as the approval of enzyme replacement therapy, have substantially changed the patients perspectives. Objectives To check for Pompe’s disease in a series of adult patients diagnosed with myopathy of unknown etiology (MUE), PM or with asymptomatic hyperCKemia. Methods Patients with high values or creatin kinase (>1000 UI/L) recruited from a general routine laboratory and patients diagnosed with PM or MUE attended in a specialized myopathies outpatient clinic from 2 tertiary University Hospitals in Barcelona during the period of 1 year (from january 2012 to january 2013) were evaluated. The diagnosis of both PM and MUE was reached after a full pathologic analysis including histochemistry and immunohistochemistry on muscle biopsies was performed. We included another group of patients with well-known myopathy as a control group. In all patients, acid α-glucosidase activity in DBS was the method employed for screening and positive cases were then confirmed by enzymatic activity in purified lymphocytes and genetic testing. Results One-hundred twenty-four patients (78 female), with a median age (SD) of 53.6 yrs (17.6) were analysed. Polymyositis was diagnosed in 25 patients, hyper CK in 9, and MUE in 50. Other well-known myopathies such as mitochondrial myopathies, dystrophinopathies, dysferlinopathies, and McArdle disease were diagnosed in the remaining 40 (control group). Eight patients (3 with polymyositis, 2 with hyperCKemia and 3 with MUE tested positive for DBS to Pompe´s disease. Only one patient from the group of MUE was confirmed to be positive for Pompe´s disease by enzymatic and genetic testing. Conclusions Pompe’s disease may be an underdiagnosed disease in patients with myopathy of uncertain origin and it should be included in the differential diagnosis in these patients. Positivity to DBS required enzymatic and genetic confirmation. References Van der Ploeg AT, Reuser AJ. Lysosomal Storage Diseases 2. Pompe´s diseases. Lancet 2008;372:1342-53. van der Beek NA, de Vries JM, Hagemans ML, et al. Clinical features and predictor for disease natural progression in adults with Pompe disease: a nationwide prospective observational study. Orphanet Journal of Rare Diseases 2012, doi: 10.1186/1750-1172-7-88. Disclosure of Interest None Declared