amyotrophies

Amyotrophies is a term used to describe a range of conditions in which skeletal muscle mass progressively declines, resulting in weakness and disability. The word derives from Greek roots meaning “no nourishment of the muscle.” In clinical use, amyotrophies encompass disorders in which muscle wasting is a prominent feature, arising from loss of motor nerve input (neurogenic causes), intrinsic muscle disease (myopathic causes), or prolonged disuse.

Causes and classification fall broadly into three groups. Neurogenic amyotrophies result from damage to motor neurons or their axons, as seen in motor neuron diseases such as amyotrophic lateral sclerosis, spinal muscular atrophy, or sequelae of poliomyelitis. Myopathic amyotrophies arise from primary muscle disorders, including muscular dystrophies and inflammatory or metabolic myopathies, where the muscle tissue itself degenerates. A third mechanism is disuse atrophy, which occurs when muscles are chronically underused due to immobilization or reduced activity, leading to muscle fiber loss and diminished strength.

Pathophysiology typically involves loss of motor units and subsequent muscle fiber atrophy. Neurogenic atrophy often shows angular fibers and fiber-type grouping on biopsy, whereas myopathic atrophy shows more uniform fiber degeneration with varying histologic patterns. Clinically, patients present with progressive muscle weakness and visible or palpable muscle wasting; reflexes may be reduced, and fasciculations can occur in neurogenic forms. Sensation is usually preserved in pure motor disorders but may be affected in certain neuropathies.

Diagnosis integrates history, physical examination, electromyography, nerve conduction studies, serum markers, imaging, and genetic or biopsy testing as indicated. Management is etiology-driven and supportive, focusing on physical therapy, nutrition, respiratory care when needed, and treatment of the underlying disease where possible. The prognosis varies with the underlying cause and disease course. See also muscle atrophy and denervation.