From exercise intolerance to functional improvement: the second wind phenomenon in the identification of McArdle disease

Abstract

McArdle disease is the most common of the glycogen storage diseases. Onset of symptoms is usually in childhood with muscle pain and restricted exercise capacity. Signs and symptoms are often ignored in children or put down to 'growing pains' and thus diagnosis is often delayed. Misdiagnosis is not uncommon because several other conditions such as muscular dystrophy and muscle channelopathies can manifest with similar symptoms. A simple exercise test performed in the clinic can however help to identify patients by revealing the second wind phenomenon which is pathognomonic of the condition. Here a patient is reported illustrating the value of using a simple 12 minute walk test.Keywords: McArdle Disease, glycogen storage disease type V, second wind phenomenon, exercise test, 12 minute walk test. RESUMO A doença de McArdle é o tipo mais frequente das glicogenoses. A apresentação clínica característica na infância inclui mialgia e intolerância aos esforços/exercício físico. Frequentemente, os sinais e sintomas das crianças não são considerados devidamente, sendo muitas vezes interpretados como "dores do crescimento", retardando o diagnóstico. Erros diagnósticos não são raros uma vez que outras doenças, como distrofia muscular ou canalopatias musculares, podem apresentar sintomas semelhantes. Entretanto, um simples teste de exercício físico realizado no ambulatório/consultório médico pode ajudar a identificar estes pacientes pois evidencia o fenômeno second wind, patognomônico da doença de McArdle. Aqui é descrito um relato de caso de um paciente ilustrando o valor do simples 12 minutes walk test.Palavras-chave: doença de McArdle, doença de depósito do glicogênio tipo V, fenomeno de second wind, teste do exercício, teste 12 minutos de marcha.

Can a Low-Carbohydrate Diet Improve Exercise Tolerance in Mcardle Disease?

“…McArdle disease is a rare disorder of skeletal muscle carbohydrate metabolism, with an estimated prevalence between 1: 100,000-1:167,000 [1]. Affected individuals have mutations in both alleles of the PYGM gene, which encodes myophosphorylase, the skeletal muscle isoform of glycogen phosphorylase.…”

Misdiagnosis is an important factor for diagnostic delay in McArdle disease

“…In children symptoms reported by parents include:• Infancy: difficulty crawling more than a few yards • Toddlers: wanting to be carried/or put in a push-chair all of the time, complaining of pain when walking • Children: ○ unable to run (maximum running distance 100 m) ○ unable to keep up with peers ○ collapse/vomiting during sporting activities Muscle contracture Severe rigidity with associated pain (patients might report it as "muscle seizes up", "severe cramp"). Muscle contracture may affect any skeletal muscle, for example the forearm, with activities such as opening cans, picking up heavy pots, carrying shopping.Second windDuring aerobic activity symptoms improve after 8-10 minutes.The second wind can be identified with functional exercise testing with cardiac monitoring such as the 12 minute walk test or cycle ergometry[7,[9][10][11].…”

Manifesting heterozygotes in McArdle disease: a myth or a reality—role of statins

“…A hallmark of McArdle disease is the second wind phenomenon, which occurs after~10 min of dynamic exercise (e.g., brisk walking, cycling) and is characterized by a sudden relief in the feelings of myalgia and breathlessness as well as in the tachycardia, which had started with exercise (Scalco et al 2014). Before the genetics of the disease was known, diagnosis was based on the results of muscle biopsies (i.e., showing absence of M-GP activity, together with abnormal subsarcolemmal glycogen stores).…”