Patient-Reported Experiences with a Low-Carbohydrate Ketogenic Diet: An International Survey in Patients with McArdle Disease

The low-carbohydrate ketogenic diet (LCKD) has attracted increased attention in recent years as a potential treatment option for individuals with McArdle disease (glycogen storage disease type V), and despite the absence of strong scientific evidence of the LCKD's benefits, increased numbers of individuals with McArdle disease have tried a LCKD. The objective of this study was to collect patient-reported experiences with a LCKD. We aimed to estimate the immediate prevalence of individuals that had tried a LCKD in an international McArdle disease cohort, and we aimed to report on the patient-reported experiences with the diet, both positive and negative. A total of 183 responses were collected from individuals with McArdle disease from 18 countries. We found that one-third of the cohort had tried a LCKD, and almost 90% experienced some degree of positive effect, with the most prominent effects on McArdle disease-related core symptoms (e.g., activity intolerance, muscle pain, and muscle fatigue). Adverse effects were rare and generally rated as mild to moderate. These patient-reported findings underline the need for randomized clinical trials to decisively determine if a LCKD is a suitable nutritional strategy for patients with McArdle disease. The results from this study can prompt and contribute to the design of such a clinical trial.

Pharmacological and nutritional treatment for McArdle disease (Glycogen Storage Disease type V)

Background 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 is an update of a review first published in 2004.Objectives To review systematically the evidence from randomised controlled trials (RCTs) of pharmacological or nutritional treatments for improving exercise performance and quality of life in McArdle disease.Search methods We searched the Cochrane Neuromuscular Disease Group Specialized Register, CENTRAL, MEDLINE and EMBASE on 11 August 2014.Selection criteria We included RCTs (including cross-over studies) and quasi-RCTs. We included 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.Data collection and analysis Three review authors checked the titles and abstracts identified by the search and reviewed the manuscripts. Two review authors independently assessed the risk of bias of relevant studies, with comments from a third author. Two authors extracted data onto a specially designed form.Main results We identified 31 studies, and 13 fulfilled the criteria for inclusion. We described trials that were not eligible for the review 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/Dangiotens in 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.Authors' conclusions 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.

Pharmacological and nutritional treatment for McArdle disease (Glycogen Storage Disease type V)

BACKGROUND

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.

OBJECTIVES

To review systematically the evidence from randomized controlled trials of pharmacological or nutritional treatments for improving exercise performance and quality of life in McArdle disease.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group Specialised Register (17 May 2010), the Cochrane Central Register of Controlled Trials (Issue 2, 2010 in The Cochrane Library), MEDLINE (January 1966 to May 2010) and EMBASE (January 1980 to May 2010) using the search terms 'McArdle disease', 'Glycogen Storage Disease type V' and 'muscle phosphorylase deficiency'.

SELECTION CRITERIA

We included randomized controlled trials (including cross-over studies) and quasi-randomised trials. Unblinded open trials and individual patient studies were included 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 (VO(2)) 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.

DATA COLLECTION AND ANALYSIS

Three review authors checked the titles and abstracts identified by the search and reviewed the manuscripts. In the first review two authors (RQ and RB) independently assessed methodological quality of relevant studies and extracted data onto a specially designed form. In this update methodological quality of data was assessed by RQ and AM with comments from BS.

MAIN RESULTS

We identified 31 studies,13 fulfilled the criteria for inclusion. Excluded trials are included in the Discussion. The largest treatment trial included 19 subjects. There was no benefit with: D-ribose, glucagon, verapamil, vitamin B(6), branched chain amino acids, dantrolene sodium, and high dose creatine. Minimal 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.

AUTHORS' CONCLUSIONS

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.

A case of McArdle disease: efficacy of vitamin B6 on fatigability and impaired glycogenolysis

McArdle disease is a glycogenetic myopathy caused by a deficit of myophosphorylase inherited in an autosomal recessive pattern. Here, we report a case of McArdle disease in which fatigability was the only subjective complaint. Objective neurological findings were normal except for very mild muscle weakness in limbs and an elevated serum creatine kinase level. Ischemic forearm exercise test showed deficient glycogenolysis. In the muscle biopsy specimen, periodic acid Schiff (PAS) stained subsarcolemmal glycogen was increased and the muscle phosphorylase A activity was decreased. After administration of vitamin B6, fatigability was diminished and ischemic forearm exercise test showed improved glycogenolysis. Vitamin B6 may be beneficial for McArdle disease, especially for its easy fatigability.

Clinical use of creatine in neuromuscular and neurometabolic disorders

Many of the neuromuscular (e.g., muscular dystrophy) and neurometabolic (e.g., mitochondrial cytopathies) disorders share similar final common pathways of cellular dysfunction that may be favorably influenced by creatine monohydrate (CrM) supplementation. Studies using the mdx model of Duchenne muscular dystrophy have found evidence of enhanced mitochondrial function, reduced intra-cellular calcium and improved performance with CrM supplementation. Clinical trials in patients with Duchenne and Becker's muscular dystrophy have shown improved function, fat-free mass, and some evidence of improved bone health with CrM supplementation. In contrast, the improvements in function in myotonic dystrophy and inherited neuropathies (e.g., Charcot-Marie-Tooth) have not been significant. Some studies in patients with mitochondrial cytopathies have shown improved muscle endurance and body composition, yet other studies did not find significant improvements in patients with mitochondrial cytopathy. Lower-dose CrM supplementation in patients with McArdle's disease (myophosphorylase deficiency) improved exercise capacity, yet higher doses actually showed some indication of worsened function. Based upon known cellular pathologies, there are potential benefits from CrM supplementation in patients with steroid myopathy, inflammatory myopathy, myoadenylate deaminase deficiency, and fatty acid oxidation defects. Larger randomized control trials (RCT) using homogeneous patient groups and objective and clinically relevant outcome variables are needed to determine whether creatine supplementation will be of therapeutic benefit to patients with neuromuscular or neurometabolic disorders. Given the relatively low prevalence of some of the neuromuscular and neurometabolic disorders, it will be necessary to use surrogate markers of potential clinical efficacy including markers of oxidative stress, cellular energy charge, and gene expression patterns.

Pharmacological and nutritional treatment for McArdle disease (Glycogen Storage Disease type V)

BACKGROUND

McArdle disease (Glycogen Storage Disease type V) is caused by the absence of the glycolytic enzyme, muscle phosphorylase. People present with exercise-induced pain, cramps, fatigue, and myoglobinuria, which can result in acute renal failure if it is severe.

OBJECTIVES

To systematically review the evidence from randomised controlled trials of pharmacological or nutritional treatments in improving exercise performance and quality of life in McArdle disease.

SEARCH STRATEGY

We updated the review by searching the Cochrane Neuromuscular Disease Group Trials Register (November 2007), MEDLINE (January 1966 to November 2007) and EMBASE (January 1980 to November 2007) using the search terms 'McArdle disease' and its synonym 'Glycogen Storage Disease type V'.

SELECTION CRITERIA

We included randomised controlled trials (including crossover studies) and quasi-randomised trials. Open trials and individual patient studies with no participant or observer blinding were included in the discussion. Types of interventions included any pharmacological agent or micronutrient or macronutrient supplementation. Primary outcome measures included any objective assessment of exercise endurance (for example aerobic capacity (VO(2)) max, walking speed, muscle force or power and improvement in fatiguability). Secondary outcome measures included metabolic changes (such as reduced plasma creatine kinase activity and a reduction in the frequency of myoglobinuria), subjective measures (including quality of life scores and indices of disability) and serious adverse events.

DATA COLLECTION AND ANALYSIS

Three review authors checked the titles and abstracts identified by the search and reviewed the manuscripts. Two review authors (RQ and RB) independently assessed methodological quality of the full text of potentially relevant studies and extracted data onto a specially designed form.

MAIN RESULTS

We reviewed 24 studies. Twelve trials fulfilled the criteria for inclusion, with two being first identified in this update. The 12 excluded trials are included in the discussion. The largest treatment trial included 19 cases. The other trials included fewer than 12 cases. As there were only single trials for a given intervention we were unable to undertake a meta-analysis.

AUTHORS' CONCLUSIONS

There is no evidence of significant benefit from any specific nutritional or pharmacological treatment in McArdle disease. In one small trial low dose creatine produced slight benefit but high dose creatine caused myalgia. Ingestion of oral sucrose immediately before exercise reduced perceived ratings of exertion and heart rate and improved exercise tolerance. This treatment will not influence sustained or unexpected exercise and may cause significant weight gain. A carbohydrate rich diet did benefit patients. Because of the rarity of McArdle disease, there is a need to develop international multicentre collaboration and standardised assessment protocols for future treatment trials.

Treatment of glycogenosys type V (McArdle disease) with creatine and ketogenic diet with clinical scores and with 31P-MRS on working leg muscle

McArdle's disease is caused by genetic defects of the muscle-specific isozyme of glycogen phosphorylase, which block ATP formation from glycogen in skeletal muscle. Creatine supplementation and ketogenic diet have been tested as potential supplements for muscle energy metabolism which may improve muscle symptomatic. Outcome measures were clinical scores describing muscle symptomatic and parameters derived from 31P-MRS examinations on working muscle. In two placebo controlled cross-over studies low dose creatine showed beneficial effects on muscle symptoms and performance whereas high dose creatine distinctly worsened muscle symptomatic in patients. In both studies, however, the absence of an elevation in phosphocreatine indicated the absence of a creatine uptake by the muscle fibre. The effects of creatine on muscle symptomatic may be independent from energy metabolism in muscle. In a case study, ketogenic diet improved muscle symptomatic and performance. However, these effects again did not result in 31P-MRS visible changes in muscle energy metabolism.

Pharmacological and nutritional treatment trials in McArdle disease

A systematic review of evidence for randomised controlled trials using pharmacologic and nutritional therapies in McArdle disease was undertaken. Primary outcome measures included any objective assessment of exercise endurance. Secondary outcome measures included changes in metabolic parameters, subjective measures such as quality of life scores and adverse outcomes. Ten randomised controlled trials were identified. Two trials low dose creatine (60 mg/kg/day) and oral sucrose 75 g prior to exercise demonstrated a positive effect.

Pharmacological and nutritional treatment for McArdle's disease (Glycogen Storage Disease type V)

BACKGROUND

McArdle's disease (Glycogen Storage Disease type V) is caused by the absence of the glycolytic enzyme, muscle phosphorylase. Patients present with exercise-induced pain, cramps, fatigue, myoglobinuria and acute renal failure, which can ensue if the myoglobinuria is severe.

OBJECTIVES

To systematically review the evidence from randomised controlled trials of pharmacological or nutritional treatments in improving exercise performance and quality of life in McArdle's disease.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group register (searched December 2001 and updated in December 2003), MEDLINE (January 1966 to December 2003) and EMBASE (January 1980 to December 2003) using the search term 'McArdle's disease and it's synonym 'Glycogen Storage Disease type V'.

SELECTION CRITERIA

We included randomised controlled trials (including crossover studies) and quasi-randomised trials. Open trials and individual patient studies with no patient or observer blinding were included in the discussion but not the review. Types of interventions included any pharmacological agent or micronutrient or macronutrient supplementation. Primary outcome measures included any objective assessment of exercise endurance (for example VO2 max, walking speed, muscle force/power and improvement in fatiguability). Secondary outcome measures included metabolic changes (such as reduced plasma creatine kinase activity and a reduction in the frequency of myoglobinuria); subjective measures (including quality of life scores and indices of disability); and serious adverse events.

DATA COLLECTION AND ANALYSIS

Two reviewers checked the titles and abstracts identified by the search, independently assessed methodological quality of the full text of potentially relevant studies and extracted data onto a specially designed form.

MAIN RESULTS

We reviewed 20 trials. Ten trials fulfilled the criteria for inclusion and ten trials were included in the discussion. The largest treatment trial included 19 cases, the other trials included fewer than 12 cases. As there were only single trials for a given intervention we were unable to undertake a meta-analysis.

REVIEWERS' CONCLUSIONS

It is not yet possible to recommend any specific treatment for McArdle's disease. Low dose creatine supplementation was shown to demonstrate a statistically significant benefit, albeit modest, in ischaemic exercise in a small number of patients. Ingestion of oral sucrose immediately prior to exercise reduces perceived ratings of exertion and heart rate and improves exercise tolerance. This treatment will not influence sustained or unexpected exercise and may cause significant weight gain. Because of the rarity of McArdle's disease, there is a need to develop multicentre collaboration and standardised assessment protocols for future treatment trials.

The effect of oral sucrose on exercise tolerance in patients with McArdle's disease

BACKGROUND

Energy metabolism in muscles relies predominantly on the breakdown of glycogen early in exercise. In patients with McArdle's disease, blocked glycogenolysis in muscles results in low exercise tolerance and can lead to muscle injury, particularly in the first minutes of exercise. We hypothesized that ingesting sucrose before exercise would increase the availability of glucose and would therefore improve exercise tolerance in patients with McArdle's disease.

METHODS

In a single-blind, randomized, placebo-controlled crossover study, 12 patients with McArdle's disease drank 660 ml of a beverage that had been sweetened with artificial sweeteners (placebo) or with 75 g of sucrose after an overnight fast. Thirty to 40 minutes later, the patients rode a stationary bicycle at a constant workload for 15 minutes while the heart rate, level of perceived exertion, and venous blood glucose levels were monitored.

RESULTS

Supplemental sucrose increased the mean plasma glucose level by more than 36 mg per deciliter (2.0 mmol per liter) and resulted in a marked improvement in exercise tolerance in all patients. The mean (+/-SE) heart rate dropped by a maximum of 34+/-3 beats per minute (P<0.001), and the level of perceived exertion fell dramatically when the patients ingested glucose as compared with when they received the placebo.

CONCLUSIONS

This study suggests that the ingestion of sucrose before exercise can markedly improve exercise tolerance in patients with McArdle's disease. The treatment takes effect during the time when muscle injury commonly develops in these patients. In addition to increasing the patients' exercise capacity and sense of well-being, the treatment may protect against exercise-induced rhabdomyolysis.

Effect of high-dose creatine therapy on symptoms of exercise intolerance in McArdle disease: double-blind, placebo-controlled crossover study

BACKGROUND

In a recent study, we showed that administration of low-dose creatine (Cr) (60 mg/kg daily) improved work capacity in patients with McArdle disease.

OBJECTIVE

To assess the efficacy of high-dose Cr therapy in McArdle disease.

DESIGN

Randomized, double-blind, placebo-controlled crossover study.

PATIENTS

Nineteen patients with McArdle disease.

INTERVENTION

Treatment with Cr, 150 mg/kg daily. Each treatment phase with Cr or placebo lasted 5 weeks.

MAIN OUTCOME MEASURES

The patient's daily rating of symptoms of exercise intolerance. At the end of each treatment phase, serum creatine and serum creatine kinase levels, phosphorus 31 magnetic resonance spectroscopy, and surface electromyograms were assessed.

RESULTS

Clinical end points revealed increases in the intensity of exercise-induced pain in working muscles (mean treatment-induced difference [d], 0.30 in log(score); 95% confidence interval [CI], 0.05-0.55; P =.02), the limitation of daily activities (d, 0.59; 95% CI, 0.22-0.97;P =.005), and body mass index (d, 0.33 kg/m2, 95% CI, 0.10-0.56 kg/m2; P =.008) with Cr use. Surface electromyograms revealed a smaller increase in the electromyographic amplitude over time during muscle contraction with Cr use (d, -13.52%/min; 95% CI, -23.71%/min to -3.34%/min; P =.01). There were no significant changes in phosphorus 31 magnetic resonance spectroscopy variables.

CONCLUSIONS

Administration of high-dose Cr worsened the main clinical symptoms of exercise intolerance in McArdle disease. These neurologic adverse effects represent a major dose-limiting factor in Cr therapy for McArdle disease. Taken together with results of a previous study, the indication for symptomatic therapy with Cr needs to be clarified. An effective Cr dosage without adverse effects may be between 60 and 150 mg/kg daily.

Creatine therapy in myophosphorylase deficiency (McArdle disease): a placebo-controlled crossover trial

OBJECTIVE

To determine whether treatment with creatine can improve exercise intolerance in myophosphorylase deficiency (McArdle disease).

DESIGN

Double-blind, placebo-controlled crossover study with oral creatine monohydrate supplementation.

PATIENTS

Nine patients with biochemically and genetically proven McArdle disease were treated.

INTERVENTION

Five days of daily high-dose creatine intake (150 mg/kg body weight) were followed by daily low-dose creatine intake (60 mg/kg). Each treatment phase with creatine or placebo lasted 5 weeks.

MAIN OUTCOME MEASURES

The effect of treatment was estimated at the end of each treatment phase by recording clinical scores, ergometer exercise test results, phosphorus 31 nuclear magnetic resonance spectroscopy, and surface electromyography.

RESULTS

Of 9 patients, 5 reported improvement of muscle complaints with creatine. Force-time integrals (P =.03) and depletion of phosphocreatine (P =.04) increased significantly during ischemic exercise with creatine. Phosphocreatine depletion also increased significantly during aerobic exercise (P =.006). The decrease of median frequency in surface electromyograms during contraction was significantly larger (P =.03) with creatine.

CONCLUSION

This is the first controlled study indicating that creatine supplementation improves skeletal muscle function in McArdle disease.

Oral branched-chain amino acids do not improve exercise capacity in McArdle disease

To determine whether oral branched-chain amino acids (BCAAs) improve exercise capacity, six fasting patients with McArdle's disease were given a solution of BCAA (77 mg/kg) or a control noncaloric beverage 30 minutes before exercise. The BCAA meal tripled plasma BCAA levels, increased BCAA catabolism as indicated by greater exercise increases in plasma glutamine and alanine, but lowered mean peak free fatty acid levels and reduced exercise capacity in five of six patients. Lower work capacity may be attributed to a net reduction in muscle fuel availability after BCAA administration.

Effect of vitamin B6 supplementation in McArdle's disease: a strategic case study

A patient-blind study into the effect of a 10-week cessation of long-term vitamin B6 supplementation on B6 status and performance in McArdle's disease is reported. Muscle performance was assessed both subjectively and objectively by an ischaemic fatiguing protocol of the adductor pollicis muscle. Nine weeks after withdrawal of supplementation, vitamin B6 status had changed from adequacy to inadequacy and the force loss during the ischaemic fatiguing protocol had increased at all frequencies studied. The patient reported decreased exercise tolerance after 7 weeks and by the tenth week was experiencing an increase in muscle cramps. Vitamin B6 status and muscle performance may be linked in McArdle's disease and there is potential for enhancement of performance by B6 supplementation.

A double blind, placebo controlled, crossover trial of D-ribose in McArdle's disease

To determine whether seven days oral D-ribose would improve exercise tolerance in a group of 5 patients with McArdle's disease, we performed a double blind placebo controlled crossover trial. Subjects performed weekly treadmill exercise tests with expired gas analysis until their times were reproducible. They then received 60 g D-ribose daily or placebo for seven days. Exercise testing was repeated on completion of this period. A seven day washout period then followed. Subjects then performed a new baseline exercise test prior to starting the other solution. Again after seven days the exercise test was repeated. There was no significant difference between pre-treatment exercise tests for peak oxygen consumption or level of leg fatigue. Patients did not like taking the ribose and D-Ribose does not appear to be of benefit to patients with McArdle's disease.

Dantrolene sodium does influence the second-wind phenomenon in McArdle's disease. Electrophysiological evidence during exercise in a double-blind placebo-controlled, cross-over study in 5 patients

Five patients with McArdle's disease entered a double-blind, placebo-controlled, cross-over study of dantrolene sodium. None of the patients experienced beneficial effect of dantrolene sodium medication. Each patient performed 2 exercise tests. Surface EMG during exercise tests without medication showed a temporary increase in EMG activity during the adaptation phase. Quite unexpectedly however, in view of the negative clinical results, this electrophysiological manifestation of muscle fatigue during the adaptation phase diminished or disappeared in all patients investigated when dantrolene sodium was used.

A double-blind, placebo-controlled, crossover study of verapamil in exertional muscle pain

Eleven patients, comprising three cases of McArdle's disease and eight with an exertional muscle pain syndrome (EMPS) of unknown cause, entered a double-blind crossover study of verapamil and placebo. None of the patients with McArdle's disease responded to verapamil, but two patients with unclassified EMPS experienced a striking improvement in symptoms and two others showed a partial response. No patient responded to placebo. Six of the eight cases with unclassified EMPS, including the four patients who responded to verapamil, had symptoms that indicated possible abnormalities of muscle metabolism, and four showed nonspecific biochemical, electromyographic, and muscle biopsy abnormalities. The two other EMPS patients had symptoms that suggested that a primary muscle disease was unlikely. They showed no laboratory evidence of muscle disorder, but had abnormal profiles on personality (MMPI) testing. Calcium antagonists, such as verapamil, may be useful in the treatment of some patients with benign exertional myalgia, but the mechanism of action of the drug in such cases is unclear.

Depot-glucagon in the treatment of McArdle's disease

Glucagon has been reported to improve exercise tolerance in some patients with myophosphorylase deficiency (McArdle's disease) but a placebo effect was not excluded in previous trials. A single-blind controlled trial of glucagon in a patient with myophosphorylase deficiency is described. Although an improved exercise endurance of the forearm muscles was demonstrated with both short-acting and depot-glucagon, this was not statistically significant when compared with placebo or no treatment.

Metabolic basis of improved exercise tolerance: muscle phosphorylase deficiency after glucagon administration

A 26-year-old girl with muscle phosphorylase deficiency had exercise intolerance and experienced an occasional "second wind" phenomenon. Muscle glycogen concentration was about three times the normal level, whereas each glycolytic intermediate below the phosphorylase step was equivalent to only 10% of a normal level. Semi-ischemic forearm exercise tests disclosed no elevation of the venous lactate or pyruvate level, but they showed remarkable increases of serum creatine kinase and ammonia. Glucagon administration markedly augmented exercise tolerance. Forearm exercise after glucagon injection significantly increased venous lactate. Thus, the beneficial effect of glucagon is attributable to blood glucose utilization by muscle.

A comparative study on glucagon effect between McArdle disease and Tarui disease

Pretreatment with glucagon relieved patients with McArdle disease from muscular symptoms during exercise and enhanced exercise performance, though it did not produce any improvement in patients with Tarui disease. The difference in glucagon effect between the two diseases was clearly demonstrated in the bicycle ergometer exercise tests. In addition, the semi-ischemic forearm exercise tests performed after glucagon injection showed that increased lactate production was significantly induced by exercise in McArdle disease, but it was not the case in Tarui disease. In McArdle disease, the augmentation in exercise-induced lactate production was also observed after administration of glucose, or glucose plus insulin, but it was neither observed after administration of insulin alone nor after arginine or epinephrine administration. These findings suggest that the beneficial effect of glucagon in McArdle disease is due to the enhanced utilization of circulating glucose through the muscular glycolytic pathway realized in the coexistence of hyperglycemia and hyperinsulinemia.

[McArdle's disease: therapeutic use of depot-glucagon]

Typical signs and findings of McArdle's disease were noted in a 27-year-old women. Echocardiographically there was impaired myocardial function. Subcutaneous injection of 2 mg depot-glucagon increased blood sugar levels with objective improvement of muscular function. This is suggested as a practical method of treatment for anticipated increase in muscular stress.