Metabolic myopathies. A diagnostic evaluation

McArdle's Disease: A Differential Diagnosis of Metabolic Myopathies

McArdle's disease, also known as glycogen storage disease type V or McArdle syndrome, is a pure muscle myopathy with an autosomal recessive inheritance pattern. It is caused by mutations in the gene that encodes muscle phosphorylase. Symptoms typically begin in late adolescence or early adulthood, presenting as exercise intolerance. This review focuses on the diagnosis of McArdle's disease, initially manifesting as a clinical picture of rhabdomyolysis in an 18-year-old male patient with a history of minor thalassemia who had been followed in pediatric consultation since age three for failure to thrive. After excluding common causes such as alcohol consumption, drug use, traumatic muscle compression, and other conditions, the diagnosis of McArdle's disease was considered. The diagnosis was supported by laboratory tests showing myoglobinuria and elevated creatine kinase levels, as well as the absence of increased serum lactate following ischemic exercise. Genetic testing confirmed the presence of mutations in the PYGM gene, corroborating the diagnosis. Treatment includes administering a diet rich in slow-absorbing carbohydrates, regular low-intensity physical exercise, and, in some cases, supplementation with vitamin B6 and creatine. The prognosis is generally favorable with proper disease management, although vigorous exercise should be avoided to prevent complications such as severe muscle injury and rhabdomyolysis. Although McArdle's disease is a rare condition, it is likely underdiagnosed. Ideally, it should be considered in the differential diagnosis of rhabdomyolysis in all patients with symptoms of exercise intolerance and/or recurrent myoglobinuria.

Hoffmann's syndrome in subclinical hypothyroidism

Hypothyroidism is an endocrine disorder which occurs due to a deficiency of thyroid hormones. Hoffmann's syndrome is a rare complication of hypothyroidism - presenting as hypothyroid myopathy. We describe the case of a 20-year-old lactating female, known to have hypothyroidism (diagnosed during her pregnancy and having discontinued treatment following delivery), presenting with complaints of pain, swelling of bilateral calf muscles with cramps in bilateral lower limbs. Symptoms of muscle pseudohypertrophy with muscle stiffness are relatively rare in subclinical hypothyroidism and it is important to identify and diagnose this rare condition, and initiate appropriate treatment.

Diagnosis of primary mitochondrial disorders -Emphasis on myopathological aspects

Mitochondrial disorders are one of the most common neurometabolic disorders affecting all age groups. The phenotype-genotype heterogeneity in these disorders can be attributed to the dual genetic control on mitochondrial functions, posing a challenge for diagnosis. Though the advancement in the high-throughput sequencing and other omics platforms resulted in a "genetics-first" approach, the muscle biopsy remains the benchmark in most of the mitochondrial disorders. This review focuses on the myopathological aspects of primary mitochondrial disorders. The utility of muscle biopsy is not limited to analyse the structural abnormalities; rather it also proves to be a potential tool to understand the deranged sub-cellular functions.

MUSCULAR HYPERTROPHY AS ATYPICAL INITIAL PRESENTATION OF HYPOTHYROIDISM

Hypothyroidism is a common endocrine disease with characteristic symptoms and signs such as fatigue, weight gain, intolerance of cold, constipation, depression, mental slowdown and muscle cramps. Myopathic changes are observed in 30-80% of patients with hypothyroidism, but muscular hypertrophy with muscle stiffness has been reported in less than 10% of patients. Hoffmann's syndrome is a specific form of the hypothyroid-associated myopathy, rarely seen. Symptoms of this syndrome include proximal muscle weakness, hypertrophies in extremities, stiffness, muscle cramps, spontaneous muscle pain; and are associated with increased muscle enzymes. These findings can be seen at any time during hypothyroidism. Hofmann's syndrome has a very good prognosis. Its response to hormone replacement therapy is very good. Therefore, in patients with myopathy-like symptoms, considering in the differential diagnosis that the myopathy may be a reflection of hypothyroidism will facilitate the diagnosis and treatment. In this case, we aimed to present together Hashimoto thyroiditis and muscular hypertrophy, which is an atypical presentation of hypothyroidism and rarely seen in the literature, namely Hoffmann's syndrome.

Hashimoto's thyroiditis presenting as Hoffman's syndrome, rhabdomyolysis and acute kidney injury

An otherwise healthy young man presented with gradual progressive fatigue for the past 12 months disturbing his daily activities. Clinical examination revealed marked generalised muscular hypertrophy including the temporalis muscles bilaterally. Investigation revealed that the patient was grossly hypothyroid due to Hashimoto's thyroiditis with rhabdomyolysis and acute kidney injury. The finding of muscle weakness and pseudohypertrophy in association with hypothyroidism is called Hoffman's syndrome. The patient was hydrated and thyroxine replacement initiated. On follow-up, the patient showed clinical as well as biochemical improvement.

Uncommon presentation of a common disorder

We report about a young male who presented with generalized muscle stiffness, involving the limb, facial, and paraspinal muscles. The stiffness was severe enough to restrict all his daily activities, progressively increased with movements and also produced recurrent falls. This clinical picture resembled one of stiff person syndrome. As he had hypertrophy of calf muscles and generalized muscle tautness he was evaluated for other disorders which can resemble stiff person syndrome. Investigations revealed severe hypothyroidism with thyroid antibodies being elevated. This case is reported to highlight the fact that myopathy as a presenting manifestation of hypothyroidism can simulate stiff person syndrome. It is essential to identify the condition early as it recovers fully with treatment. Our patient responded well to thyroid replacement therapy and was able to lead a normal life.

A young lady with swelling and stiffness of calf muscles

Hypothyroidism causes a variety of changes in the body. Though uncommon, hypothyroidism can present as myopathy. Hoffman's syndrome is a specific, rare form of hypothyroid myopathy, which causes proximal weakness and pseudohypertrophy of muscles.

Metabolic myopathies: update 2009

Metabolic myopathies are inborn errors of metabolism that result in impaired energy production due to defects in glycogen, lipid, mitochondrial, and possibly adenine nucleotide metabolism. Fatty acid oxidation defects (FAOD), glycogen storage disease, and mitochondrial myopathies represent the 3 main groups of disorders, and some consider myoadenylate deaminase (AMPD1 deficiency) to be a metabolic myopathy. Clinically, a variety of neuromuscular presentations are seen at different ages of life. Newborns and infants commonly present with hypotonia and multisystem involvement (liver and brain), whereas onset later in life usually presents with exercise intolerance with or without progressive muscle weakness and myoglobinuria. In general, the glycogen storage diseases result in high-intensity exercise intolerance, whereas the FAODs and the mitochondrial myopathies manifest predominately during endurance-type activity or under fasted or other metabolically stressful conditions. The clinical examination is often normal, and testing requires various combinations of exercise stress testing, serum creatine kinase activity and lactate concentration determination, urine organic acids, muscle biopsy, neuroimaging, and specific genetic testing for the diagnosis of a specific metabolic myopathy. Prenatal screening is available in many countries for several of the FAODs through liquid chromatography-tandem mass spectrometry. Early identification of these conditions with lifestyle measures, nutritional intervention, and cofactor treatment is important to prevent or delay the onset of muscle weakness and to avoid potential life-threatening complications such as rhabdomyolysis with resultant renal failure or hepatic failure. This article will review the key clinical features, diagnostic tests, and treatment recommendations for the more common metabolic myopathies, with an emphasis on mitochondrial myopathies.

[Hoffmann syndrome presenting to the emergency department]

We report a case of hypothyroid myopathy, or Hoffmann syndrome, in a 31-year-old man who presented to the emergency department with asthenia, muscular pain, cramps, and joint pain. Tests revealed increased creatine phosphokinase level (8102 U/L) and severe hypothyroidism (content of T4=3.8 pg/ml, T3=1.3 pg/ml, and thyrotropin stimulating hormone>150 microU/ml). Other causes of myopathy were excluded by anamnestic investigation and paraclinical exam. Treatment was begun with thyroid hormones (from 75 to 175 microg) and good clinical evolution was rapid. The pathophysiology of hypothyroid myopathy, clinical aspects and pathologic anatomic elements are described. The exact etiology of hypothyroidism must be known because some pathologic features are benign and treatment can have good results, whereas others, such as cancer, have worse prognosis.

Equine metabolic myopathies with emphasis on the diagnostic approach comparison with human myopathies A review

This review gives an overview of the presently known human and equine metabolic myopathies with emphasis on the diagnostic approach. Metabolic myopathies are muscle disorders caused by a biochemical defect of the skeletal muscle energy system, which results in inefficient muscle performance. Myopathies can arise in different levels of the metabolic system. In this review the metabolic myopathies are categorized in disorders of the carbohydrate metabolism, lipid metabolism, mitochondrial myopathies (other than those described in lipid metabolism), disorders of purine metabolism, primary disorders involving ion channels and electrolyte flux and secondary or acquired metabolic myopathies.

Grandpa and I have dystrophinopathy?: approach to asymptomatic hyperCKemia

This report describes three males from a single kinship, ages 7, 8, and 67 years with clinically asymptomatic dystrophinopathy. The index case was an 8-year-old male evaluated for asymptomatic but persistently elevated serum creatine kinase levels. Muscle biopsy demonstrated a mild myopathy, without necrotic fibers. Immunostaining for dystrophin revealed a slight reduction in sarcolemmal reactivity for the amino terminus of dystrophin. Dystrophin gene analysis revealed a deletion of exon 45 to exon 51. Genetic analysis identified two other affected males (age 7 years and 67 years), as well as four female carriers in the same family. The 7-year-old male had mildly increased creatine kinase levels with normal muscle strength. The 67-year-old grandfather had normal neuromuscular examination and serum creatine kinase levels. Asymptomatic dystrophinopathy in late adulthood is exceptionally rare, and highlights the importance of consideration of dystrophin mutation analysis in patients with hyperCKemia, even in the absence of muscle weakness.

Malignant hyperthermia and myotonic disorders

Advances in physiology and molecular genetics have promoted greater understanding of the various clinical manifestations of muscle disorders. For example, myotonia or profound weakness may be observed in sodium channel disease (e.g., paramyotonia congenita or hyperkalemic periodic paralysis), depending on the specific channel defect or with slight changes in membrane potential. Observed effects of anesthetic techniques have been essential to elucidating the primary muscular nature of myotonia. Commonly used anesthetic medications have potentially lethal (e.g., MH) or serious (e.g., myotonic dystrophy) adverse effects. Conversely, lidocaine or propofol may have therapeutic benefit for patients with skeletal muscle sodium channel disorders. Additional investigation is required to improve our understanding of how age, gender, or other factors determine the phenotypic expression of malignant hyperthermia. Future research holds the promise for more accurate pre-anesthetic identification of persons with heritable myopathies, especially those who are asymptomatic. Enhanced awareness of multiple organ system involvement in myotonic dystrophy is essential for planning perioperative care. Patients with periodic paralysis require that we know factors that incite or inhibit the development of their attacks. Advances in bench research and detailed clinical studies will further improve our ability to provide optimal care for patients with muscle disorders.

Genetic diseases of muscle

In the last twenty years, the genetic basis for most of the inherited myopathies and muscular dystrophies has been unveiled. Diseases have been found to result from loss of function of structural components of the muscle basal lamina (e.g., MCD1A), sarcolemma (e.g., the sarcoglycanopathies), nucleus (e.g., EDMD) and sarcomere (e.g., the nemaline myopathies). A few have been associated with abnormalities in the genes for muscle enzymes (e.g., calpain and fukutin). Alternate mechanisms of pathogenesis have also recently been suggested by mutations lying outside of coding regions, such as the "field effect" of chromosomal mutations in DM2. In the future, we will likely identify the genes responsible for the remaining disorders, including many of the distal myopathies. In addition, we may also find skeletal muscle diseases associated with some of the presently non-implicated muscle proteins: syntropin, dystrobrevin, epsilon-sarcoglycan and sarcospan. The next steps may be to identify and understand the relationship of modifier genes producing the phenotypic heterogeneity of many of these diseases and to characterize those and other targets for therapeutic intervention, whether by gene therapy or by pharmacological treatment.