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

[McArdle's disease revealed by acute low back pain]

INTRODUCTION

McArdle disease, or glycogen storage disease type V (GSD 5), is a rare metabolic myopathy linked to an autosomal recessive myophosphorylase deficiency.

CASE REPORT

We report the case of a 17-year-old male patient who was referred to the emergency department for the management of acute inflammatory low back pain, without traumatic context, associated with an increase of CK at 66,336 UI/L (N<192UI/L) and a CRP at 202mg/L. The immunological assessment was negative and the spinal MRI showed images in favor of necrotizing fasciitis affecting the erector spinae muscles, among others. Faced with the description of difficulties in practicing physical activities since childhood and a non-ischaemic forearm exercise test showing no elevation in lactacidemia, genetic tests were carried out, finding two heterozygous variants in the PYGM gene: c.1963G>A (p.Glu655Lys) class 5 and c.2178-1G>A class 4, confirming the diagnosis of McArdle disease.

DISCUSSION

GSD 5 is a disease characterized essentially by muscular fatigability during exercise. The case reported here is original in the clinical circumstances leading to the diagnosis, i.e., inaugural acute low back pain with rhabdomyolysis. This symptomatology had already been described before, but in a patient whose diagnosis was already known. Spinal MRI showed non-specific muscle inflammation and necrosis. Muscle biopsy only found necrosis but no pathological elements typical of the diagnosis. If the symptoms are suggestive, it may be preferable to directly perform a non-ischaemic forearm exercise test, in order to go directly to molecular genetic analysis. There is no specific curative treatment of GSD 5. However, some measures can be implemented to limit the symptoms, such as learning physical exercises, limiting intense efforts and adopting dietary recommendations.

Toward an Understanding of GSD5 (McArdle disease): How Do Individuals Learn to Live with the Metabolic Defect in Daily Life

BACKGROUND

Glycogen storage disease type 5 (GSD) is an autosomal recessive inherited metabolic myopathy caused by a deficiency of the enzyme muscle glycogen phosphorylase. Individuals with GSD5 experience physical activity intolerance.

OBJECTIVE

This patient-led study aimed to capture the daily life experiences of GSD5, with a focus on adapting to and coping with their physical activity intolerance.

METHODS

An online survey was composed in close collaboration with patient organizations. It consisted of customized and validated questionnaires on demographics, general health and comorbidities, physical activity, psychosocial well-being and functioning, pain, fatigue and adapting to and coping with GSD5.

RESULTS

One hundred sixty-two participants (16 countries) participated. The majority, n = 86 (69%) were from the Netherlands, USA or UK. We observed a high rate of misdiagnosis prior to GSD5 diagnosis (49%), surprisingly a relatively high proportion had not been diagnosed by DNA testing which is the gold standard. Being diagnosed had a strong impact on emotional status, daily life activities and important life choices. A large proportion had not received any rehabilitation (41%) nor medical treatment (57%) before diagnosis. Engagement in vigorous and moderate physical activity was reduced. Health related quality of life was low, most likely related to low physical health. The median Fatigue Severity Score was 4.3, indicating moderate to severe fatigue. Participants themselves had found various ways to adapt to and cope with their disability. The adaptations concerned all aspect of their life, including household chores, social and physical activities, and work. In addition to lack of support, participants reported limited availability of information sources.

CONCLUSION

Participants have provided guidance for newly diagnosed people, including the advice to accept one's limited abilities and maintain an active lifestyle. We conclude that adequate counseling on ways of adapting and coping is expected to increase both health-related quality of life and physical activity.

Fatigue and associated factors in 172 patients with McArdle disease: An international web-based survey

McArdle disease is an autosomal recessive inherited disease caused by pathogenic variants in the PYGM gene, resulting in virtual absence of the myophosphorylase enzyme in skeletal muscle. Patients experience physical activity intolerance, muscle pain, and muscle fatigue. This study aimed to investigate other fatigue domains with the Multidimensional Fatigue Inventory (MFI-20) along with an investigation of potential contributing factors, including relevant disease and lifestyle-related factors. We conducted a survey in an international cohort of patients with McArdle disease. The survey included questions on demographics and McArdle disease-related symptoms, and the questionnaires: MFI-20, Insomnia Severity Index (ISI), and International Physical Activity Questionnaire Short-Form (IPAQ-SF). One hundred seventy-four responses were included in the data analyses. We found relatively high fatigue scores in all five domains (general fatigue (12.9 ± 2.2), mental fatigue (10.1 ± 4.1), physical fatigue (13.7 ± 4.1), reduced activity (12.1 ± 4.1), and reduced motivation (10.4 ± 3.4)). Fatigue associated with McArdle symptom severity (p < 0.005), lower levels of physical activity (assessed by IPAQ-SF) (p < 0.05), and poor sleep (assessed by ISI) (p < 0.05). These findings call for clinical focus and future research into fatigue, sleep and mental health in patients with McArdle disease.

Can a modified ketogenic diet be a nutritional strategy for patients with McArdle disease? Results from a randomized, single-blind, placebo-controlled, cross-over study

BACKGROUND

McArdle disease is caused by myophosphorylase deficiency leading to blocked glycogenolysis in skeletal muscle. Consequently, individuals with McArdle disease have intolerance to physical activity, muscle fatigue, and pain. These symptoms vary according to the availability of alternative fuels for muscle contraction. In theory, a modified ketogenic diet (mKD) can provide alternative fuels in the form of ketone bodies and potentially boost fat oxidation.

METHODS

This randomized, single-blind, placebo-controlled, cross-over study aimed to investigate if a mKD improves exercise capacity in individuals with McArdle disease. Participants were randomized to follow a mKD (75-80% fat, 15% protein, 5-10% carbohydrates) or placebo diet (PD) first for three weeks, followed by a wash-out period, and then the opposite diet. The primary outcome was change in heart rate during constant-load cycling. Secondary outcomes included change in plasma metabolites, perceived exertion, indirect calorimetry measures, maximal exercise capacity, and patient-reported outcomes.

RESULTS

Fifteen out of 20 patients with genetically verified McArdle disease completed all study visits, and 14 were included in the data analyses. We found that the mKD induced a metabolic shift towards increased fat oxidation (∼60% increase), and a 19-fold increase in plasma β-hydroxybutyrate (p < 0.05). The mKD did not improve heart rate responses during constant-load cycling but did improve patient-reported outcomes and maximal exercise capacity (∼20% increase) compared to the PD.

CONCLUSION

The mKD did not alleviate all McArdle disease-related symptoms but did induce some positive changes. To date, no satisfactory treatment options exist other than exercise training. To that end, a mKD can be a possible nutritional strategy for some individuals with McArdle disease who are motivated to undertake a restrictive diet.

CLINICAL TRIAL REGISTRATION

clinical trials.gov: NCT04044508.

Metabolic Myopathies in the Era of Next-Generation Sequencing

Metabolic myopathies are rare inherited disorders that deserve more attention from neurologists and pediatricians. Pompe disease and McArdle disease represent some of the most common diseases in clinical practice; however, other less common diseases are now better-known. In general the pathophysiology of metabolic myopathies needs to be better understood. Thanks to the advent of next-generation sequencing (NGS), genetic testing has replaced more invasive investigations and sophisticated enzymatic assays to reach a final diagnosis in many cases. The current diagnostic algorithms for metabolic myopathies have integrated this paradigm shift and restrict invasive investigations for complicated cases. Moreover, NGS contributes to the discovery of novel genes and proteins, providing new insights into muscle metabolism and pathophysiology. More importantly, a growing number of these conditions are amenable to therapeutic approaches such as diets of different kinds, exercise training protocols, and enzyme replacement therapy or gene therapy. Prevention and management-notably of rhabdomyolysis-are key to avoiding serious and potentially life-threatening complications and improving patients' quality of life. Although not devoid of limitations, the newborn screening programs that are currently mushrooming across the globe show that early intervention in metabolic myopathies is a key factor for better therapeutic efficacy and long-term prognosis. As a whole NGS has largely increased the diagnostic yield of metabolic myopathies, but more invasive but classical investigations are still critical when the genetic diagnosis is unclear or when it comes to optimizing the follow-up and care of these muscular disorders.