Prueba de ejercicio con isquemia en el antebrazo. Estandarización y valor diagnóstico en la identificación de la enfermedad de McArdle

BACKGROUND AND OBJECTIVE

The forearm ischemic exercise test (FIET) with serial lactate determinations is used worldwide for the screening of McArdle's disease and other glucogenosis. Yet there is no uniformity with regard to the intensity of the work and the ischemia time. The aim of this study was to standardize the test conditions in normal people and to check its efficacy in our population.

PATIENTS AND METHOD

In a first stage, we included 9 healthy persons in whom four different conditions were applied regarding the cuff pressure and ischemia time. In a second stage, 5 previously known McArdle disease patients, 30 normal individuals and 25 patients with a diagnosis of myopathy other than glucogenosis underwent FIET with the conditions standardized in the first stage.

RESULTS

The best curve profile was obtained with a cuff pressure 20 mm Hg above systolic blood pressure and with exercise until fatigue o cramps without time limitation. With a cut-point at 200% of the basal values of ammonium and lactate, the sensitivity and specificity of FIET were 100% and 96%, respectively, for McArdle's disease. No major side effects were recorded in any case.

CONCLUSIONS

Conditions of FIET have been standardized. Taking into account the high sensitivity and specificity of the test, its use should be considered in the screening of anaerobic metabolic myopathies.

[Analysis of 12 cases of McArdle's disease diagnosed after 30 years]

PURPOSE

McArdle's disease (MAD) or glycogen storage disease type V, usually starts in childhood or adolescence. Generally diagnosis is made before the early adulthood because patients present well defined syndrome and are constrained.

METHOD

We retrospectively investigated all MAD cases diagnosed in the biochemical laboratory from Debrousse Hospital in Lyon, during 40 years (1962-2002). We then selected patients whose diagnosis had been made after 30 years.

RESULTS

Fifteen patients answered our criteria but only 11 files could be analysed. A twelfth patient (service of internal medicine--Royan) supplemented the series. We sought the reasons of a late diagnosis: early age of beginning but few symptoms (7 cases), age of beginning higher than 20 years (5 cases including 3 after 45 years). The principal symptoms were muscular deficit and muscular pains (8 cases) and second wind phenomenon (7 cases). Creatinine phosphokinase level was constantly high. Ischemic effort test when it was carried out was constantly abnormal. Conversely electromyogram was often normal (5 cases). Several biopsies were necessary in a third of the cases to evoke the diagnosis, particularly among the patients with late onset symptoms.

CONCLUSION

Diagnosis of metabolic MAD is generally easy if the interrogation finds inaugural symptoms in childhood or adolescence even if the patient consults very late in the life. The diagnosis can become much more difficult if it begins late in life (atypical symptoms, need for several muscular biopsy).

McArdle's disease presenting as recurrent cryptogenic renal failure due to occult seizures

Myophosphorylase deficiency (McArdle's disease) may present with episodic renal failure following exertion. We present a case of adult-onset myophosphorylase deficiency in which recurrent bouts of renal failure could not be associated with any exertional events until a tonic seizure was witnessed after the fourth episode of renal failure. In the absence of a clear exertional cause for myoglobinuria, an occult seizure disorder should be suspected.

A diagnostic cycle test for McArdle's disease

We investigated whether the second wind phenomenon (ie, a decrease in heart rate and perceived exertion during exercise) is pathognomonic for McArdle's disease. Twenty-four patients with McArdle's disease, 17 healthy subjects, and 25 patients with other inborn errors of muscle metabolism cycled a constant workload for 15 minutes. In McArdle's disease patients, heart rate consistently decreased by 35 +/- 3 beats per minute from the 7(th) to the 15(th) minute of exercise, whereas heart rate increased progressively with exercise in all 42 control subjects. The findings indicate that cycling at a moderate, constant workload provides a specific, sensitive, and simple diagnostic test for McArdle's disease.

[Rhabdomyolysis and myoglobinuria]

Rhabdomyolysis is a disorder characterized by acute damage of the sarcolemma of the skeletal muscle leading to release of potentially toxic muscle cell components into the circulation, most notably creatine phosphokinase (CK) and myoglobin, and is frequently accompanied by myoglobinuria. Therefore, the term myoglobinuria is often used interchangeably with the term rhabdomyolysis. This disorder may result in potential life-threatening complications such as acute myoglobinuric renal failure, hyperkalemia and cardiac arrest, disseminated intravascular coagulation, and compartment syndrome. The condition is etiologically heterogeneous and may result from a large variety of diseases affecting muscle membranes, membrane ion channels, and muscle energy supply including acquired causes (e.g., exertion, crush injury and trauma, alcoholism, drugs, and toxins) and hereditary causes (e.g., disorders of carbohydrate metabolism, disorders of lipid metabolism, or diseases of the muscle associated with malignant hyperthermia). In many patients with idiopathic recurrent rhabdomyolysis, specific inherited metabolic defects have not been recognized up to now.

[Nation-wide survey on muscle glycogen storage disease (MGSDs) and comparison with our experiences in diagnosis of MGSDs]

To clarify the actual frequency of each type of muscle glycogen storage diseases (MGSDs) in Japan, we performed nation-wide survey in 2001. We compared the results with our diagnostic experiences at Hamamatu City Medical Center for Developmental Medicine. The majority (approximately 80%) of the MGSDs consisted of type II, V and III in Japan. In our experiences, most of the patients were diagnosed by the assays of glycolytic enzyme activities using biopsied skeletal muscles. However, the biochemical diagnoses of MGSDs type II, III, IV, and IX can be made using blood samples. Additionally, common genetic mutation (708/709 delTTC) of myophosphorylase gene has been found approximately in 50% of the Japanese patients with MGSDs type V. Therefore, approximately 70% of the MGSDs may be diagnosed by biochemical and genetic analysis using blood samples. Additional survey on McArdle's disease showed that the onset of muscle symptoms in McArdle's disease were variable, however, fixed muscular symptoms such as muscle weakness and muscle atrophy were present in 45% of patients.

A nonischemic forearm exercise test for McArdle disease

Ischemic forearm exercise invariably causes muscle cramps and pain in patients with glycolytic defects. We investigated an alternative diagnostic exercise test that may be better tolerated. Nine patients with McArdle disease, one with the partial glycolytic defect phosphoglycerate mutase deficiency, and nine matched, healthy subjects performed the classic ischemic forearm protocol and an identical protocol without ischemia. Blood was sampled in the median cubital vein of the exercised arm. Plasma lactate level increased similarly in healthy subjects during ischemic (Delta5.1 +/- 0.7mmol L(-1)) and non-ischemic (Delta4.4 +/- 0.3) tests and decreased similarly in McArdle patients (Delta-0.10 +/- 0.02 vs Delta-0.40 +/- 0.10mmol L(-1)). Postexercise peak lactate to ammonia ratios clearly separated patients and healthy controls in ischemic (McArdle, 4 +/- 2 [range, 1-12]; partial glycolytic defect phosphoglycerate mutase deficiency, 6; healthy, 33 +/- 4 [range, 17-56]) and non-ischemic (McArdle, 5 +/- 1 [range, 1-10]; partial glycolytic defect phosphoglycerate mutase deficiency, 5; healthy, 42 +/- 3 [range, 35-56]) protocols. Similar differences in lactate to ammonia ratio between patients and healthy subjects were observed in two other work protocols using intermittent handgrip contraction at 50% and static handgrip exercise at 30% of maximal voluntary contraction force. All patients developed pain and cramps during the ischemic test, and four had to abort the test prematurely. No patient experienced cramps in the non-ischemic test, and all completed the test. The findings indicate that the diagnostic ischemic forearm test for glycolytic disorders should be replaced by an aerobic forearm test.

A direct StyI polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) test for the myophosphorylase mutation in cattle

Myophosphorylase deficiency in cattle is a muscle disease induced by a C-->T point mutation in codon 489 of the myophosphorylase gene, which until now has only been diagnosed in the Charolais breed. The disease seems to be inherited in an autosomal monogenic recessive manner. A calf of double muscled phenotype was suspected of suffering from myophosphorylase deficiency based on typical symptoms, i.e. brown-coloured, transparent urine, occurring after exercise; exercise intolerance; symptoms of pain; and an elevated level of plasma creatine kinase. The presence of the previously described mutation was excluded using a newly developed, improved polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) procedure to identify easily heterozygous carriers and homozygous affected animals.

A forearm exercise screening test for mitochondrial myopathy

BACKGROUND

The authors hypothesized that impaired oxygen extraction in mitochondrial myopathy (MM) results in a high oxygen saturation in venous effluent blood from working muscle and that this phenomenon can be used as a diagnostic tool for MM.

METHODS

Twelve patients with MM, 10 patients with muscular dystrophy, and 12 healthy subjects were studied. All subjects performed intermittent static handgrip exercise (1/2 Hz) at 40% of maximal voluntary contraction (MVC) for 3 minutes. Cubital venous oxygen saturation and brachial artery flow were measured in the exercised arm.

RESULTS

Exercise-induced venous oxygen desaturation was smaller in patients with MM (Delta - 7 +/- 5%) than in subjects with muscular dystrophy (Delta - 38 +/- 2%; p = 0.00001) and healthy subjects (Delta - 43 +/- 2%; p = 0.0000002). MVC and exercise blood flow were similar in patients with MM (18 +/- 3 kg; 436 +/- 65 mL/min) and patients with muscular dystrophy (15 +/- 3 kg; 460 +/- 85 mL/min), but were higher in healthy subjects (32 +/- 4 kg; 630 +/- 58 mL/min; p < 0.03). In seven patients with MM and seven patients with McArdle disease, studied with a slightly different protocol, exercise-induced oxygen desaturation was also impaired in MM (Delta - +/- 5%) compared with McArdle disease (Delta - 26 +/- 3%; p = 0.007).

CONCLUSION

Oxygen desaturation in venous blood from exercising muscle is markedly lower in patients with mitochondrial myopathy than in subjects with other muscle diseases and healthy subjects, suggesting that a forearm exercise test can be a diagnostic screening tool for mitochondrial myopathy.

A new stop codon mutation (Y52X) in the myophosphorylase gene in a Greek patient with McArdle's disease

We identified a novel stop codon mutation in the myophosphorylase gene in a Greek patient with typical symptoms of McArdle's disease. This is the first genetic study of myophosphorylase deficiency in a Greek family, showing that the proband was a compound heterozygous for the common "caucasian" mutation (R49X) and a new nonsense mutation (Y52X), both within exon 1. The new point mutation, a C-to-G transversion at codon 52, converts an encoded tyrosine to a stop codon. Our study confirms that the R49X is also present in the Greek population. The Y52X may represent a private mutation or a common mutation among Greeks. Our data further expand the already remarkable genetic heterogeneity of McArdle's disease. The prevalence of the Y52X mutation in Greek patients with McArdle's disease remains to be determined.

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.

Glycogenosis type V (McArdle's disease) mimicking atypical myositis

A 13-year-old girl was referred to our clinic because of a positive rheumatoid factor test, muscle pain and weakness. Laboratory evaluation revealed an increased ESR, hypergammaglobulinaemia, antinuclear antibodies, circulating immune complexes, complement consumption and elevated serum creatine kinase (CK) activity. A needle biopsy of the dolent muscle showed normal routine histology. Immunohistochemistry disclosed single lymphocytes and a weak myocytic HLA class I expression. The diagnosis of myositis was considered and corticosteroids were initiated, leading to an increase of complement levels and a decrease of CK-activity and ESR. She subjectively felt stronger but still reported exercise intolerance and metabolic myopathy was considered. Myophosphorylase activity was completely lacking, establishing the diagnosis of McArdle's disease. CK level was found to be elevated in an obese 4-year-old brother too, who refused extensive walking but reported no muscle pain. Myophosphorylase deficiency was demonstrated by histochemistry and by biochemical analysis of his muscle. The female case illustrates that in children with the clinical picture of inflammatory myopathy and serological but not clinical response to therapy underlying metabolic muscle disorders should be excluded. Since the pathogenesis of polymyositis remains unclear, we speculate that inflammatory changes observed in the muscles may have been initiated by muscular damage resulting from the underlying metabolic disease. The serological changes remained unexplained and may contribute to a so far undeterminable connective tissue disease.

Adult-onset exercise intolerance due to phosphorylase b kinase deficiency

Muscle-specific phosphorylase b kinase deficiency is an unusual form of glycogen storage disorder. The majority of patients are male with an age at diagnosis between 15 to 36 years. Clinical features include exercise intolerance, myalgia and muscle weakness. A forearm ischaemic exercise test is usually normal and histochemical staining for myophosphorylase positive. The demonstration of reduced muscle phosphorylase b kinase activity by biochemical assay confirms the diagnosis. We report a 36 year old male with phosphorylase b kinase deficiency and symptom onset in adult life.

[McArdle disease: report of four brothers with myophosphorylase deficiency]

Myophosphorylase deficiency, or McArdle disease, is an uncommon entity. The gene for human myophosphorylase has been cloned and is located on chromosome 11, in keeping with the autosomal recessive nature of the disease and there is an excess of male patients. The diagnosis is established by documentation of elevated glycogen content and reduced phosphorylase activity in biopsied muscle tissue. We report four cases with McArdle disease which were 16, 15, 11 and 5 years old. They were brothers, and they came to the hospital because of pain, cramps and myoglobinuria after exercise or infection; in the first case, a male patient, myoglobinuria caused acute renal failure. Three of them showed reduced phosphorylase activity in biopsied muscle tissue. We discuss the different therapeutic possibilities.

Rhabdomyolysis triggered by an asthmatic attack in a patient with McArdle disease

We describe a patient with McArdle disease who developed rhabdomyolysis triggered by a bronchial asthmatic attack. A 64-year-old man had chronic pulmonary emphysema with asthma, and an asthmatic attack led to severe rhabdomyolysis that required continuous hemodiafiltration. After 2 years, a physical examination revealed atrophy of the extremities compared with previous examinations, especially of the intercostal muscles. During that time, he suffered two severe bronchial asthmatic attacks. His serum level of creatinine kinase remained between 4,000 and 7,000 IU/l when he did not suffer from asthmatic attacks and rhabdomyolysis had abated. Therefore, we suspected that his recent muscle atrophy was caused by asthmatic attacks, and discussed the possibility of his respiratory muscle weakness due to McArdle disease in relation to his severe bronchial asthmatic attacks as well as chronic obstructive pulmonary disease.

A homozygous missense mutation (A659D) in the myophosphorylase gene in a Spanish patient with McArdle's disease

We identified a novel missense mutation in the myophosphorylase gene (PYGM) in a Spanish patient with McArdle's disease. This homozygous C-to-A mutation results in the replacement of a highly conserved alanine at amino acid position 659 with an aspartic acid in the C-terminal domain of the myophosphorylase gene protein, near binding sites for pyridoxal phosphate and glucose. Our data further expand the genetic heterogeneity in patients with McArdle's disease.

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.

Molecular diagnosis of McArdle disease: revised genomic structure of the myophosphorylase gene and identification of a novel mutation

McArdle disease is a rare autosomal recessive disorder of the muscle glycogen metabolism caused by mutations in the muscle glycogen phosphorylase gene. Until now, a total number of 11 different mutations in the coding region or splice sites of the myophosphorylase gene have been identified. In contrast to a wealth of data on the RNA and protein level, little information is available on the genomic sequence of the corresponding gene. To facilitate molecular diagnosis of McArdle disease, we reinvestigated the genomic structure of the myophosphorylase gene and sequenced about 9.8 kilobases (kb) on the genomic level. By choosing 14 intronic primer pairs, we were able to amplify the complete human coding sequence as well as the adjacent splice sites of the 20 exons. Direct sequencing of the amplification products of a consanguineous Turkish family with typical McArdle disease revealed a novel single base pair deletion in exon 18, which predicts a frameshift and a premature termination of the protein. In summary, we established a system for molecular diagnosis of McArdle disease based on a revised genomic structure of the myophosphorylase gene and demonstrated its feasibility by identification of a novel mutation.

[McArdle's disease in a 14-year-old girl with fatigability and raised muscle enzymes]

INTRODUCTION

McArdle's disease is a disorder of muscle energy metabolism caused by a deficit of muscle phosphorylase. The typical form presents with fatigability muscle cramps and pains triggered by physical exercise. Some cases have few symptoms. We report the case of a 14 year old girl diagnosed on finding a significantly raised CPK, studied following her complaint of fatigability.

CLINICAL CASE

A 14 year old girl presented with a CPK of 1,243 UI/l (normal 10-32) which had been requested in view of her fatigability. She had never had cramps, muscle pains or dark urine. Neurological examination was normal. The levels of CPK after intense exercise on the previous days were 7,459 UI/l, and after rest for one week were 283 UI/l (normal 25-230). The ischemic exercise test showed that she was unable to finish the test, with flat lactate and pyruvate curves and markedly raised ammonia (basal 89 and maximum 571 micrograms/dl). On muscle biopsy, the morphology of the striated muscle was seen to be normal and staining for myophosphorylase was negative.

CONCLUSIONS

The fluctuations of muscle enzyme levels in relation to exercise orientate the diagnosis towards a disorder of muscle energy metabolism. To detect this, the investigation should be carried out following severe exercise for several days and then compared with a further test after some days of rest. The ischemic exercise test permits identification of defects of glycogenolysis, orientating the choice of suitable histochemical, enzymatic or molecular biological tests.