Familial Myoplegia

FAMILIAL MYOPLEGIA (from Greek mys- muscle and plege- strike) (syn. myoplegia periodica, s. familialis, myoplegia paroxysmalis congenita, paroxysmal paralysis, periodic paralysis of the limbs, dystrophia myoplegica), a rare familial disease of the nervous system, characterized by periodic attacks of paralysis of the limbs with diminished reflexes and temporary loss of electrical excitability of the paralyzed muscles. After an attack, all phenomena disappear completely, and during the interictal state, no abnormalities can be detected in the neuromuscular system. The disease was first described by Shakhnovich (1882) under the name "intermittent paraplegia"; in his case, the father and son were affected. Later (1885), Westphal provided a detailed description of the disease, followed by Oppenheim. Cousot (1886) noted the hereditary nature of the disease. M. is a clearly hereditary disease. In some families, it has been traced through 5 generations. Type of inheritance - monohybrid dominant (Fig. 1). Men are affected somewhat more often than women (according to Schmidt's material - 64% men). In women, attacks of M. appear to occur in a milder form or are less frequent. Sometimes skips of generations were observed (Fig. 2), which led Schmidt to make an obviously incorrect assumption about the possible recessive nature of inheritance. Skips of generations occur somewhat more often in women. Thus, the type of inheritance should be defined as: dominant, partially limited to the male sex. The disease is quite evenly distributed in different countries, everywhere remaining relatively very rare. Apparently, it occurs somewhat more frequently in Japan.

Patho-anatomically, in cases that came to autopsy, normal condition of the nervous system and very slight changes in muscle tissue (increase in the number of sarcolemma nuclei, changes in the caliber of muscle fibers) were found. The same was also found in several cases on biopsy. The interstitial tissue in the muscles was normal. No inflammatory changes were found. The essence of the disease is not yet fully clear. Some assumed a temporary loss of function of the anterior motor horns of the spinal cord either due to temporary vascular anemia or due to temporary poisoning by some unknown toxin (Bornstein); however, the complete loss of electrical excitability of the muscles during an attack of M. contradicts this assumption, and the localization of the lesion began to be correctly sought in the damage to the muscle fiber itself; they accused either vascular spasm (Nonne, Schmidt) or periodic auto-intoxication (Goldflam). Hypotheses about the role of the endocrine system were also expressed (Shino^aki). Mankovsky, finding great analogies between M. and myopathy, assumes that in M. there is a disorder of the central vegetative innervation, leading to episodic muscle dysfunction, similar to that which is characteristic of dystrophia muscularis progressiva in a persistent state. The details of the pathogenesis are thus still far from clear. The disease usually begins at 10-15 years of age, sometimes earlier, even from the first years of life; the first attacks are usually mild, then gradually become more severe; sometimes the attacks gradually weaken or even disappear completely with the development of involutionary phenomena. However, in other observations, the disease began late, for example, in the 6th decade. Attacks recur either with a certain regularity or completely irregularly. The intervals between them reach several months; sometimes attacks are more frequent, sometimes almost daily.

Fig. 1. Family with hereditary myoplegia described by Mankovsky.

Fig. 2. Family with hereditary myoplegia described by Schmidt.

Attacks of myoplegia usually develop at night or in the morning after sleep. Predisposing moments are very diverse: attacks have been observed after emotional stress, after physical rest (intense muscular work, according to many observations, prevents attacks).

(which protects against the attack), after cooling, alcohol, sleepless nights and especially after an increased intake of food; according to some observations, fatty or sweet food was particularly harmful, as well as eating at night; with a long-term diet, many patients were freed from attacks for a long time. Kramer established a precise dietary regimen under which his patient did not develop attacks. Shinosaki attributed the primary role to carbohydrates. However, the connection between attacks and diet is not observed in all cases. Much less frequently, hunger can trigger attacks of M., and patients should eat an enhanced dinner before bed to avoid a nocturnal attack; in one observation, this peculiarity was characteristic of all members of the affected family (Davidenkov). Many patients note that paralytic attacks develop in them predominantly at a certain time of year. Pregnancy and childbirth in a number of observations had a favorable effect on the course of the disease. The duration of each attack ranges from several hours to 1-2 days. The muscles of the limbs, trunk (the diaphragm is not paralyzed), and neck are paralyzed. The voice becomes weak; the functions of other cranial nerves are not affected; consciousness always remains clear. In isolated cases, however, the picture is complicated by paresis or paralysis of the swallowing and facial musculature and even paralysis of individual external eye muscles. In a number of observations, the proximal muscles were more severely affected than the distal ones. In milder attacks, only the muscles of the limbs are paralyzed (sometimes only the lower ones). A hemiplegic type was very rarely observed. The tone of the paralyzed muscles is always reduced. Often, pressure on the muscles during an attack is painful. Reflexes (tendon, as well as periosteal and cutaneous) disappear or are diminished; knee reflexes are often more severely affected than Achilles reflexes. The excitability of nerve trunks and muscles to galvanic and inductive current disappears or is quantitatively sharply reduced ('cadaveric reaction'). Kramer, as well as Popov, observed myasthenic reaction during an attack (Figure 3). Mechanical muscle excitability also disappears. Attacks are often accompanied by a number of vasomotor symptoms (redness or paleness of the face, cold extremities), a decrease in temperature, sweating, salivation; the Ashner symptom is sharply pronounced; patients experience thirst, nausea, a feeling of heat; sometimes during an attack, oliguria is observed, which is then followed by increased diuresis; the act of urination itself may be difficult. Sometimes mydriasis and a sluggish pupillary reaction were observed. Mankovsky established angiospasm by capillaroscopy. Often, an attack is accompanied by bradycardia, tachycardia, or arrhythmia, and according to many authors, also an expansion of the heart borders, glycosuria (Kramer). Sensitivity is always preserved. Painful paresthesias in the extremities are not uncommon. The attack gradually subsides. Patients still experience a feeling of fatigue and weakness for some time, sometimes aching in the limbs, but objective examination reveals no deviations. However, in some observations, muscle weakness and reduced excitability persisted for quite some time after the attack, and in other cases, more persistent changes in muscles were noted, either in the form of particularly voluminous athletic musculature or (which is particularly interesting from the point of view of possible pathogenetic closeness of both syndromes) in the form of gradual development of atrophic myopathy. Some patients, along with developed attacks, also have rudimentary ones, expressed only in temporary weakness and mild fatigue of the limb muscles, however, not preventing walking and complex movements. Diagnosis of familial cases is not difficult. Sporadic cases, however, are probably often overlooked. In terms of differential diagnosis, one should consider periodic paralyses in malaria, which usually have the character of central paralyses, last only a few hours, are accompanied by profuse sweating, differ in regular periodicity, and respond to treatment with quinine. Temporary paralyses of hysterical origin are not accompanied by changes in reflexes and excitability; it is usually possible to detect other hysterical symptoms (anesthesias); the provoking role of emotional stress, characteristic of M., often leads to diagnostic error. Sometimes it is difficult to distinguish an attack of M. from ascending paralysis of Landry, especially if it is not known that similar attacks have occurred before. The paralytic equivalents of epilepsy, which are still insufficiently studied, can apparently give a picture close to M.; according to some authors, some cases published under the heading of paroxysmal paralysis had exactly this origin. - The prognosis is poor for recovery, but good for life for the vast majority of cases. Only in isolated observations, very severe attacks, complicated by some extraneous factor (alimentary poisoning), ended fatally with symptoms of paralysis of the respiratory musculature. - We do not yet know of rational therapy. Schmidt saw long-term improvement from prescribing Calcium chlorate. In cases with clear alimentary provocation, it is possible to prevent attacks by prescribing the appropriate (each time special) dietary regimen.