Muscle Weakness: Clinical Meaning

Hyperthyroidism

Hyperthyroidism occurs when the thyroid gland produces too much thyroid hormone, speeding up metabolism. It causes weight loss, rapid heartbeat, anxiety, tremors, and heat intolerance. Graves' disease is the most common cause.

Multiple Sclerosis

Multiple sclerosis is a chronic autoimmune disease in which the immune system attacks the myelin sheath of nerve fibers in the central nervous system. It causes episodes of neurological symptoms including vision loss, muscle weakness, balance problems, and cognitive changes.

Amyotrophic Lateral Sclerosis (ALS)

ALS is a rapidly progressive neurodegenerative disease affecting motor neurons, causing progressive muscle weakness, paralysis, and respiratory failure. Most patients die within 3-5 years of diagnosis; riluzole and edaravone modestly slow progression.

Peripheral Neuropathy

Peripheral neuropathy results from damage to peripheral nerves, causing numbness, tingling, burning pain, and weakness in the hands and feet. Diabetes, alcohol, vitamin B12 deficiency, and chemotherapy are common causes.

Myasthenia Gravis

Myasthenia gravis is an autoimmune neuromuscular disease causing fluctuating muscle weakness, typically worsening with activity. Antibodies against acetylcholine receptors at the neuromuscular junction impair signal transmission; treatment includes cholinesterase inhibitors and immunosuppressants.

Polymyositis

Polymyositis is an inflammatory myopathy causing progressive proximal muscle weakness, elevated muscle enzymes, and abnormal electromyography. Unlike dermatomyositis, it lacks the characteristic skin findings; treatment includes corticosteroids and immunosuppressants.

Dermatomyositis

Dermatomyositis is an inflammatory myopathy with characteristic skin manifestations including heliotrope rash around the eyes and Gottron's papules over the knuckles, combined with proximal muscle weakness. It is associated with increased cancer risk.

Mixed Connective Tissue Disease

Mixed connective tissue disease (MCTD) has overlapping features of lupus, scleroderma, and polymyositis, associated with high titers of anti-U1-RNP antibodies. Pulmonary hypertension is a major complication.

Testosterone Deficiency (Low T)

Testosterone deficiency (hypogonadism) in men causes fatigue, decreased libido, erectile dysfunction, mood changes, and loss of muscle mass. Causes include aging, pituitary disorders, and testicular disease; hormone replacement therapy is the primary treatment.

Vitamin D Deficiency

Vitamin D deficiency impairs calcium absorption and bone mineralization, causing bone pain, muscle weakness, fatigue, and increased fracture risk. It is extremely common globally due to limited sun exposure and dietary insufficiency.

Hypercalcemia

Hypercalcemia is elevated blood calcium, most commonly caused by overactive parathyroid glands or cancer. Symptoms follow the mnemonic 'bones, stones, groans, and psychic moans'.

Adrenal Insufficiency

Adrenal insufficiency occurs when adrenal glands fail to produce sufficient cortisol. Primary (Addison's disease) is from adrenal damage; secondary is from pituitary or hypothalamic dysfunction.