Disorders of the Muscular System

The muscular system involves muscles, tendons, and other tissue responsible for locomotion, posture, and stability in the human body. The disorders affecting the muscular system are due to genetic, autoimmune, neurological, metabolic, or trauma-related causes. These disorders vary in type-from mild ones creating discomfort to severe functional impairments leading to difficulties with locomotion, posture, and overall function of the body.

1.0Muscular Dystrophies

• Muscular dystrophies are a heterogeneous group of genetic disorders all characterized by a progressive weakness and degeneration of skeletal muscles. 
• The most common 3 forms include the following. 

Duchenne Muscular Dystrophy (DMD) 

• Cause: Most common form; mutation in the dystrophin gene on the X chromosome 
• Symptoms: Muscle weakness originating from the lower limbs with delayed motor skills, pseudohypertrophy of calf muscles, and difficulty in walking, generally manifests in early childhood between 3-5 years.
• Course: In advanced stages, involves the heart and respiratory muscles with life-threatening complications

Becker Muscular Dystrophy (BMD)

• Cause: A less severe mutation in the dystrophin gene.
• Symptoms: Generally similar to Duchenne but starting later and developing at a much slower rate
• Course: Patients may remain ambulatory into their 40s and beyond, but ultimate cardiopulmonary involvement is common.

Myotonic Dystrophy

• Cause: Genetic mutation involving either the DMPK or CNBP genes.
• Symptoms: The condition may present with muscle wasting, cataracts, heart conduction abnormalities, and myotonia, which is the inability of muscles to relax after contraction.
• Progression: The disease has a slow progressive course with impairment of many systems, including skeletal and smooth muscles, the heart, and the endocrine system. 

Myasthenia Gravis (MG) Cause

• Cause: Autoimmune disorder characterized by destruction of acetylcholine receptors in the NMJ, which results in impaired muscle contraction. 
• Symptoms: Muscle weakness which worsens with activity and increases with rest, drooping eyelids (ptosis), difficulty swallowing, breathing problems, and generalized muscle fatigue.
• Diagnosis: Antibody tests (anti-AChR), electromyography, and response to acetylcholinesterase inhibitors.
• Treatment: Acetylcholinesterase inhibitors, immunosuppressive drugs, thymectomy (in cases of thymoma) and, in severe cases, plasmapheresis.

Amyotrophic Lateral Sclerosis (ALS)

• Cause: Degeneration of motor neurons in brain and spinal cord. Exact cause unknown, though familial cases associated with mutations in the SOD1 gene.
• Symptoms include progressive muscle weakness, fasciculation, and spasticity. It leads to paralysis, difficulty in speaking, swallowing, and breathing.
• Progression: The disease is rapidly progressive, usually leading to death within 3-5 years following diagnosis due to respiratory failure. However, in the majority of cases, cognitive functions remain preserved.
• Treatment: No cure is available, but drugs like Riluzole and Edaravone slow the disease.

Polymyositis and Dermatomyositis

• Cause: Autoimmune-mediated inflammation of muscles in polymyositis and muscle/skin inflammation in dermatomyositis.

Symptoms:

• Polymyositis: Symmetrical muscle weakness, typically proximal involvement such as shoulders and hips.
• Dermatomyositis: Same kind of muscle weakness but with skin rash-additional findings include heliotrope rash around eyes, Gottron's papules on knuckles.
• Diagnosis: Muscle biopsy with inflammation, increased muscle enzymes like creatine kinase, and autoantibodies like anti-Jo-1.
• Treatment: Corticosteroids, immunosuppressive agents like methotrexate or azathioprine, and physical therapy.

Rhabdomyolysis

• Cause: Rapid muscle breakdown with release of myoglobin into the circulation may cause renal injury. Trauma, severe exercise, drugs such as statins, infections, and dehydration are the causes. 
• Symptoms Muscle ache, swelling, dark coloured urine due to myoglobin, and weakness. 
• Complications AKI, hyperkalemia, and metabolic acidosis. 
• Diagnosis Rise in CK and myoglobin levels, presence of myoglobinuria when urine tests are performed. 
• Treatment Aggressive intravenous fluids and electrolyte management; in severe cases, dialysis is considered. 

Fibromyalgia

• Cause: The cause is unknown but is considered a central nervous system disorder involving abnormalities in processing pain. 
• Symptoms: Chronic diffuse musculoskeletal pain, fatigue, cognitive symptoms ("fibro fog"), sleep disturbances, and tenderness at specific points. 
• Diagnosis: Clinical criteria often with tenderness at 11 of 18 specific points. 
• Treatment: Pain management (NSAIDs, pregabalin, duloxetine), cognitive behavioral therapy, exercise, and strategies for improvement in sleep. 

Myopathies

• Myopathies are disorders of muscle tissue not arising from damage to the nervous system, rather by the presence of weakness and dysfunction.

1. Congenitally Myopathies

• Cause: Genetic mutation to the muscles' fibrils. For example, nemaline myopathy and central core disease.
• Symptoms: Muscle weakness, hypotonia (floppy baby syndrome). The achievement of motor milestones is retarded.

2. Metabolic Myopathies

• Cause: Genetic defect in one of several enzymes required for energy production in muscles, for instance, glycogen storage diseases such as McArdle's disease; mitochondrial myopathies.
• Symptoms: Exercise intolerance, cramps, muscle pain, and, in extreme exacerbations, rhabdomyolysis.

Compartment Syndrome

• Cause: Increased pressure within a closed muscle compartment, usually after trauma, fractures, or burns impairs blood flow and nerve function.
• Symptoms: Severe pain, swelling, tightness in the affected area, paresthesia, and reduced pulse distal to the injury.
• Diagnosis: Measurement of intracompartmental pressures.
• Treatment: Fasciotomy to relieve pressure.

1. Tetanus

• Cause: Bacterial infection by Clostridium tetani, which elaborates a neurotoxin that affects motor neurons.
• Symptoms: Muscle stiffness, spasms (especially in the jaw—"lockjaw"), difficulty swallowing, and respiratory problems.
• Prevention: Vaccination (Tetanus toxoid).
• Treatment: Antitoxins, muscle relaxants, and antibiotics.

2. Cramps and Spasms

• Cause: Involuntary contraction of the muscles may result from overuse, dehydration, electrolyte imbalances, or prolonged muscle strain.
• Symptoms: Sudden painful tightening of the muscles, usually affecting the legs or feet.
• Treatment: Stretching, hydration, electrolyte balance, and sometimes muscle relaxants.

2.0Diagnosis and General Management

• Diagnosis of muscle disorders typically includes the following:,
• Clinical Examination: The clinical examination involves looking at muscle weakness, muscle atrophy, fasciculations, and reflex changes.
• Blood Tests: CK level, autoimmune markers, and genetic testing. 
• Electromyography (EMG): Evaluates the electrical activity of muscles and nerve interaction. 
• Muscle Biopsy: For histological examination. 
• Imaging: MRI and ultrasound can detect muscle damage or inflammation. 

3.0Treatment 

• Medications: Anti-inflammatory drugs, immunosuppressants, and disease-modifying treatments. 
• Physiotherapy: To maintain muscle function and avoid atrophy. 
• Surgery: In cases like compartment syndrome or when there is a need for structural repair. 
• Supportive Care: Respiratory support, aids to mobility, nutritional management.