McArdle disease (Glycogen Storage Disease type V) is caused by an absence of muscle phosphorylase leading to exercise intolerance, myoglobinuria rhabdomyolysis and acute renal failure. This update of a review first published in 2004, systematically examined the evidence from randomised controlled trials (RCTs) of pharmacological or nutritional treatments for improving exercise performance and quality of life in McArdle disease. The Cochrane Neuromuscular Disease Group Specialized Register, CENTRAL, MEDLINE and EMBASE were searched on 11 August 2014. RCTs (including cross-over studies) and quasi-RCTs were included as well as unblinded open trials and individual patient studies in the discussion. Interventions included any pharmacological agent or nutritional supplement. Primary outcome measures included any objective assessment of exercise endurance (for example aerobic capacity (VO2) max, walking speed, muscle force or power and fatigability). Secondary outcome measures included metabolic changes (such as reduced plasma creatine kinase and a reduction in the frequency of myoglobinuria), subjective measures (including quality of life scores and indices of disability) and serious adverse events. A total of 31 studies were identifiend, 13 of which fulfilled the criteria for inclusion. Trials not eligible for the review were described in the Discussion. The included studies involved a total of 85 participants, but the number in each individual trial was small; the largest treatment trial included 19 participants and the smallest study included only one participant. There was no benefit with: D-ribose, glucagon, verapamil, vitamin B6, branched chain amino acids, dantrolene sodium, and high-dose creatine. Minimal subjective benefit was found with low dose creatine and ramipril only for patients with a polymorphism known as the D/D angiotensin converting enzyme (ACE) phenotype. A carbohydrate-rich diet resulted in better exercise performance compared with a protein-rich diet. Two studies of oral sucrose given at different times and in different amounts before exercise showed an improvement in exercise performance. Four studies reported adverse effects. Oral ribose caused diarrhoea and symptoms suggestive of hypoglycaemia including light-headedness and hunger. In one study, branched chain amino acids caused a deterioration of functional outcomes. Dantrolene was reported to cause a number of adverse effects including tiredness, somnolence, dizziness and muscle weakness. Low dose creatine (60 mg/kg/day) did not cause side-effects but high-dose creatine (150 mg/kg/day) worsened the symptoms of myalgia. Although there was low quality evidence of improvement in some parameters with creatine, oral sucrose, ramipril and a carbohydrate-rich diet, none was sufficiently strong to indicate significant clinical benefit.
