The Aging Neuromuscular System

Abstract

Symptoms and signs suggestive of neuromuscular dysfunction are very common in old age but do not necessarily indicate definable neurologic disease. The frail, wasted hands seen in an 80-year-old person may, as in a younger patient, indicate a diabetic neuropathy or amyotrophic lateral sclerosis (ALS), but after investigation the clinician is often left with the conclusion that this finding is simply due to "old age." Frequently, the cause is multifactorial, and neuromuscular function may be influenced by disorders affecting various levels of the neuraxis, as well as by disease and age-related factors outside the nervous system, such as changes in cardiopulmonary function, nutrition, and the endocrine system. Often the distinction between age changes and disease is blurred and consequently a different approach is required in assessing abnormal neurologic findings.Common symtoms reported by the elderly are muscle weakness, slowness of movement, fatigue, impaired fine coordination, muscle pain and cramps, loss of or disordered sensation, and pain. On examination, frequent findings are muscle wasting and weakness, loss of sensation, hypersensitivity, areflexia, and orthostatic hypotension. CHANGES IN THE NEUROMUSCULAR SYSTEM IN NORMAL AGING THE SENSORY UNITClinical studies have shown an increase with age in touch-pressure thresholds in the index fingeri and impairment of cutaneous thermal discriminati~n.~ Vibration sense diminishes after the age of 50 years, especially in the feet,3 and there is commonly a decline in proprioceptive f e e d b a~k .~ Special senses, including smell, taste, and hearing, also deteriorate with age, but discussion of these is beyond the scope of this review. Pathologic changes at various levels of the peripheral or central nervous system could account for the abnormalities in sensation and, for example, impaired vibration sense in the feet could be due to loss of pacinian corpuscles, demyelination of peripheral nerves, nerve root disease, spondylosis, impaired blood supply to the spinal cord, or dysfunction in central sensory systems. It is likely, however, that the primary sensory neuron or the peripheral receptors, or both, are principally involved (see Spencer and 0choa5 for review). The neuronal cell bodies in dorsal root ganglia and cranial ganglia show structural changes or drop-out with age and consequently there is loss of their nerve fibers in peripheral nerves, sensory roots, and posterior columns. Lumbosacral roots are more affected than cervical roots. Morphologic studies of peripheral nerves reveal increased evidence in old age of demyelination and, more particularly, remyelination, and also degeneration of unmyelinated and myelinated fibers and "empty" Schwann cell columns.' These changes in peripheral nerves are reflected by abnormalities on nerve conduction tests. The amplitude of sensory action potentials decreases from the third decade, and there is a lesser decline in conduction velocities, this being more pronounced across segments subject to chronic entrapment. Measure...

Pharyngeal Constriction in Elderly Dysphagic Patients Compared with Young and Elderly Nondysphagic Controls

“…These assumptions are based on studies documenting the results of aging on the mammalian neuromuscular system. Changes in muscle with age appear to be associated with disuse atrophy and support the hypothesis that only minor changes in the muscles of the oropharynx, used constantly for swallowing, can be attributed to aging alone [1,5,6]. Systemic factors, rather than normal aging, may be important in explaining muscular weakness and fatigue seen in the elderly.…”

Effects of antioxidants on contracting spinotrapezius muscle microvascular oxygenation and blood flow in aged rats

“…Their role in skeletal muscle fibers is to allow for an action potential to be transported from one region to another region allowing for a muscle contraction. There is also a decrease in the ability of motor axons and nerve muscular junctions to function properly that occurs with aged humans and animals (5,71). Any alterations within the muscle fiber to produce action potentials could produce a decrease in skeletal muscle contractile function.…”

Hyoid Movement During Swallowing in Older Patients With Dysphagia

“…However, changes in muscles with age appear to be associated with disuse atrophy, which supports the hypothesis that only minor changes in the muscles of the oropharynx, used constantly for swallowing, can be attributed to aging alone. 1,11,12 Systemic factors, rather than normal aging, may be important in explaining muscular weakness and fatigue seen in older persons. On the other hand, the older control group in this study, in whom clear differences from the younger controls were identified, took no medication and denied other medical problems.…”