Can hyperuricemia predict glycogen storage disease (McArdle's disease) in rheumatology practice? (Myogenic hyperuricemia).

Gout disease is an inflammatory arthritis that arises due to the accumulation of monosodium urate crystals (MSU) around the joints and in tissues. Clinical manifestation of metabolic diseases leading to secondary hyperuricemia most predominantly occurs in the form of gouty arthritis. Hyperuricemia and gout may develop during the course of glycogen storage diseases (GSD), particularly in GSD type I, which involves the liver. On the other hand, during the course of GSD type V (GSDV, McArdle's disease), which merely affects the muscle tissue due to the deficiency of the enzyme myophosphorylase, hyperuricemia and/or gout is rarely an expected symptom. These patients may mistakenly be diagnosed as having idiopathic hyperuricemia and associated gout, leading to the underlying secondary causes be overlooked and thus, diagnostic delays may occur. In this case report, we present a premenopausal female patient who experienced flare-ups of chronic arthritis while on disease-modifying antirheumatic drugs and intraarticular steroids due to a diagnosis of undifferentiated arthritis. The patient was initially suspected of having gouty arthritis because elevated concentrations of uric acid were incidentally detected, but then, a diagnosis of asymptomatic GSDV was made owing to elevated concentrations of muscle enzymes during colchicine use. Our aims were to remind rheumatologists of the phenomenon of "myogenic hyperuricemia" and to discuss the potential causes of hyperuricemia that develop during GSD along with the available literature.