Neurological consequences of protein and protein-calorie undernutrition

Malnutrition is a worldwide problem of enormous magnitude. The growth of the central nervous system in human beings is retarded in case of malnutrition in the very early part of life. Likewise, the peripheral nerves in infants and children and young growing animals appear susceptible to nutritional deprivation including protein as well as protein-calorie deficiency. Motor weakness, hypotonia, and hyporeflexia in infants and children are the essential clinical neurological signs in protein-calorie malnutrition (PCM). Motor and sensory nerve conduction are significantly impaired in children with PCM as well as in animals subjected to protein or protein-calorie deficiency. Histological studies have revealed reduced diameter of myelinated nerve fibers, retardation of myelination, segmental demyelination and remyelination, axonal degeneration, and shortened longitudinal growth of internodes. Diffusion barrier by perineurium may be broken. There is reduction in myelin lipids and impaired synthesis of myelin as shown by the biochemical and radioisotope incorporation studies. Presence of cholesterol esters in the biochemical synthesis of nerves suggests degeneration changes. Experimental studies have revealed that most effects of PCM on peripheral nerves can be reversed by nutritional rehabilitation, although complete recovery in the sensory nerve action potential, fiber size of dorsal nerve roots, and myelin-specific lipids does not occur. Skeletal muscle also shows many changes including muscle fiber atrophy, reduction in duration and amplitude of motor unit potentials, and/or fibrillation on electromyography (EMG) and biochemical estimation of muscle enzymes. These changes may be the reflection of a direct effect of PCM on muscles or secondary to the abnormal structural or biochemical changes in the peripheral nerves. PCM affects the central nervous system, especially the neuropsychological functions, in a lasting manner. Learning deficits and impairment of manual dexterity are the most obtrusive features. Neurotransmitter abnormalities and maturation lag in electroencephalogram have been demonstrated in experimental animals. Spinal cord dysfunction sometimes manifests overtly as clinical myelopathy. Degenerative changes in the cerebellum have been noted.