Muscle Cramps and Stiffness Stiffness: continuous muscle contraction at rest. Cramps (spasms): transient, painful, involuntary contraction of muscle or group of muscles; lasts seconds to minutes. Causes listed in Table…

Myoglobinuria Acute muscle necrosis leads to gross pigmenturia (brown) with myoglobin in urine. Also termed rhabdomyolysis. Most important syndromes in Table 129.1. Hereditary Myoglobinuria Identified Enzyme Deficiencies Genetic defect identified…

Congenital Myopathies Primary manifestation: delayed motor milestones. Congenital Muscular Dystrophies Congenital myotonic dystrophy, congenital muscular dystrophies: muscle destruction, replacement by fat and connective tissue on muscle biopsy. Congenital muscular dystrophies…

Familial Periodic Paralysis Episodic bouts of limb weakness. Inherited “channelopathies” (inherited abnormalities of ion channels). Clinical features in Table 127.1. Hypokalemic Periodic Paralysis (HoPP) Serum potassium decreases in spontaneous attack…

Progressive Muscular Dystrophies General Considerations Definition Characteristics of progressive muscular dystrophy: (1) myopathy (by clinical, histologic, and EMG criteria); (2) all symptoms are effects of muscle weakness; (3) symptoms become…

Identifying Disorders of the Motor Unit Motor unit: anterior horn cell, peripheral motor nerve, muscle. Manifestations: flaccid weakness, wasting, depression of tendon reflexes (Table 125.1). Tests to distinguish neurogenic from…

Acute Quadriplegic Myopathy Also known as “critical illness myopathy.” Corticosteroids, nondepolarizing neuromuscular blocking agents, or both considered the prime inciting factors. Condition may appear in critically ill patients without exposure…

Botulism and Antibiotic-Induced Neuromuscular Disorders Botulism Toxin blocks nicotinic and muscarinic cholinergic synapses by impeding presynaptic release of acetylcholine. Blocks fusion of vesicles with surface membrane. Epidemiology: toxin produced by…

Lambert-Eaton Myasthenic Syndrome Lambert-Eaton myasthenic syndrome (LEMS): autoimmune disease of peripheral cholinergic synapses. Small-cell lung carcinoma in 60%; other tumors in 7%. Neurologic symptoms precede those of tumor. Pathogenesis: antibodies…

Myasthenia Gravis Disorder of neuromuscular transmission from antibody-mediated attack on nicotinic AChR at neuromuscular junctions. Fluctuating weakness improved by inhibitors of cholinesterase. Etiology and Pathogenesis Polyclonal IgG antibodies to AChR…