Disorders of Muscle Disease and Neuromuscular Junction

Vocabulary flashcards covering classification, biochemical mechanisms, diagnostic tests, and clinical features of muscle diseases and neuromuscular junction disorders.

Myopathies

A wide range of conditions or muscle diseases that affect the muscles.

Duchenne Muscular Dystrophy (DMD)

The most common and severe form of muscular dystrophy, which primarily affects boys due to an X-linked recessive inheritance pattern and leads to progressive muscle weakness.

Dystrophin

A protein encoded by a gene on the X chromosome that helps strengthen muscle fibers and protect them from injury.

Biochemical Basis of DMD

Mutations in the dystrophin gene cause defective dystrophin protein, allowing excess calcium to penetrate the sarcolemma, activating proteolytic enzymes and causing mitochondrial dysfunction with ROS production, leading to chronic inflammation, fibrosis, and loss of function.

Endocrine Myopathies

Muscle disorders associated with endocrine dysfunctions, including Thyrotoxic Myopathy, Hypothyroid Myopathy, and Cushing's Syndrome.

Metabolic Myopathies

Muscle diseases caused by metabolic defects, including Glycogen Storage Diseases (e.g., McArdle disease), Fatty Acid Oxidation defects (e.g., Carnitine Palmitoyltransferase II Deficiency), and Mitochondrial Myopathies.

Mitochondrial Myopathies

Group of disorders affecting muscles due to mitochondrial dysfunction, where decreased ATP synthesis causes accumulation of toxic excess acyl-CoA, depletion of Krebs cycle intermediates, and increased free radical formation and lipid peroxidation.

Myasthenia Gravis (MG)

An autoimmune disorder characterized by weakness and rapid fatigue of voluntary muscles due to autoantibodies blocking acetylcholine receptors (AChR) at the neuromuscular junction.

Anti-MuSK Antibodies

Autoantibodies targeted against muscle-specific protein kinase, present in approximately $40\%$ of seronegative Myasthenia gravis patients.

Ptosis

Drooping of one or both eyelids, recognized as an ocular symptom of Myasthenia gravis.

Diplopia

Double vision, an ocular symptom associated with Myasthenia gravis.

Edrophonium Test

A diagnostic laboratory test for Myasthenia gravis involving administration of edrophonium chloride, a short-acting cholinesterase inhibitor, to demonstrate temporary improvement in muscle strength.

Pyridostigmine

An anticholinesterase agent used as a medication to increase the amount of acetylcholine at the neuromuscular junction in Myasthenia gravis.

Plasmapheresis

A medical procedure used in the management of Myasthenia gravis to remove circulating autoantibodies from the blood.

Thymectomy

Surgical removal of the thymus gland, performed as a surgical treatment option for Myasthenia gravis.

Simple Diagnostic Tests for Muscle Diseases

Initial laboratory investigations including urea and electrolytes, creatine kinase activity, myoglobin, activity of liver enzymes, endocrine function tests, calcium, glucose, ketone bodies, and lactate.

Specialized Diagnostic Tests for Muscle Diseases

Targeted investigations including ischemic lactate exercise testing and urinary organic acids.

Highly Specialized Diagnostic Tests for Muscle Diseases

Advanced diagnostic procedures including muscle biopsy, electromyography, mitochondrial biochemical analysis, and gene analysis for defects in glycogen metabolism, fatty acid oxidation, or mitochondrial oxidation.