Myatonia

MYATONIA (from the Greek mys - muscle and atonia - weakness, flaccidity) (synonyms: amyotonia congenita, Oppenheim's disease), described by Oppenheim (1900), is a congenital disease usually manifesting from the first days of life and expressed by a sharp limitation and often complete absence of active movements. In rarer cases, parents notice the presence of this disease only after several weeks or even months, when it is time for the child to grasp things with their hands or hold their head up, sit up, or walk. In some cases, the disease is revealed only after some intercurrent illness—pneumonia, diarrhea, dysentery (Kozhevnikov and Molchanova). Sometimes mothers indicate that during pregnancy they felt almost or even completely no movements of the fetus. The etiology and pathogenesis of the disease are unknown to this day. The disease is congenital, but apparently not familial, although cases of illness in brothers and sisters have been described. Regarding pathogenesis, various hypotheses exist. Oppenheim believes that the matter lies in the congenital underdevelopment of muscles, either independent or dependent on a delay in the development of the gray matter of the spinal cord, its anterior horns. Abrikosov and Arkhangelsky believe that the basis of the pathogenesis of myatonia is the underdevelopment of muscle tissue, either independent or connected with the underdevelopment of the entire peripheral motor neuron. Marburg considers myatonia to be the result of intrauterine poliomyelitis, and Bernhard considers polyneuritis to be its cause. Rothmann, Cavengt, and others identify myatonia with Werdnig-Hoffmann progressive spinal muscular atrophy. Others seek the cause of the disease in endocrine glands [Baudouin and Concetti in the thyroid gland, and Spiller in the thymus]. Finally, some express the assumption that the basis of myatonia is an intrauterine intoxication of an endogenous nature, perhaps products of improper metabolism in the body of the mother and fetus. The number of anatomo-pathological studies is relatively small. Some authors found only changes in the muscles; muscle fibers are very thin, have a 'hyalinoid' appearance; in them, an increase in the number of muscle nuclei and proliferation of connective tissue can be detected (Spiller). Abrikosov and Arkhangelsky found a decrease in the number of nerve cells in the anterior horns and an almost complete absence of large cells; the number of nerve fibers is also reduced, some of them lack a myelin sheath; in the anterior roots and peripheral nerves, there are many unmyelinated fibers and empty neurilemmas; all muscles are very thin due to the extreme thinness of the muscle fibers comprising them; neither phenomena of gradual atrophy of muscle fibers, nor multiplication of nuclei, nor proliferation of interstitial connective and adipose tissues were found. Kaumheimer found changes not only in the gray matter of the spinal cord but also of the medulla oblongata, and in the peripheral nerves and muscles the changes were identical to those in spinal myopathies. In symptomatology, movement disorders come to the first place. Active movements in the limbs, especially in the lower ones, are very limited or even absent. The muscles of the trunk and neck are also very weak; due to this muscle weakness, sick children not only do not walk, but do not stand, do not sit, do not hold their heads up, and almost or not at all grasp objects with their hands. Facial muscles are affected rarely. Cases of strabismus have been described, but it is apparently accidental and has no connection with the underlying disease. Sometimes the intercostal muscles also participate in the pathological process, as a result of which respiration is hindered. The diaphragm, masticatory, and swallowing muscles apparently never suffer. Upon objective examination, first of all, sharp hypotonia or even complete atonia of the muscles attracts attention. This atonia makes it possible to produce passive movements in a significantly increased volume compared to the norm. Sometimes dangling joints are noted, and sometimes secondary contractures. Upon palpation, the muscles turn out to be thin, flabby, sluggish, but severe muscle atrophy usually does not occur. False and true hypertrophies are always absent, but sometimes well-developed subcutaneous tissue hides the emaciation of the muscles, and the limbs appear normal.

Mechanical excitability is sharply reduced or absent altogether. Fibrillary twitches never occur. Tendon reflexes are either sharply reduced or absent; cutaneous and mucosal reflexes are preserved." The electrical excitability of muscles is reduced for both types of current. Collier and Wilson note that in some cases, with a sharp decrease in excitability to the faradic current, excitability to the galvanic current was either slightly reduced or not reduced at all—the myatonic or amyotonic reaction. Chenet noted precisely the opposite phenomenon. Reactions of degeneration usually do not occur. Disturbances of sensitivity, sense organs, sphincters, and the psyche, as well as significant vasomotor disorders, usually do not occur. In typical cases, the diagnosis does not present great difficulties; it is necessary to exclude acute poliomyelitis, Werdnig-Hoffmann type progressive spinal muscular atrophy, multiple neuritis, hematomyelia, etc. A careful analysis of the development of the disease, objective examination data, and the course of the disease ensures a correct diagnosis. The prognosis for myatonia is not particularly favorable. With the participation of the intercostal muscles in the process, death often occurs from intercurrent diseases of the lungs and bronchi; according to Tobler, in 33% of cases, these diseases are the cause of death. Intercurrent diseases always worsen the condition of patients. In favorable cases, the disease regresses over the years, and significant improvement sometimes occurs: patients begin to walk independently and manage without outside help.—Therapy for myatonia is not entirely powerless: electrization, massage, and passive gymnastics should occupy the first place. Strengthening and tonic treatment is recommended: iron, phosphorus, fish oil, etc. In some cases, improvement from the use of calcium salts was noted.