Intellectual Impairment in Muscular Dystrophy

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The association of intellectual retardation with childhood muscular dystrophy was noted many years ago. Duchenne (1872) thought that 5 of his 13 cases were retarded. Gowers (1879). on the other hand, found evidence of mental retardation in only 2 of his 24 patients, and he thought that it was not a feature of the muscle disease but that there was probably a higher incidence of muscular dystrophy in mentally retarded children. In Erb's (1891) review of 83 cases of muscular dystrophy there are 25 whose case histories conform to the Duchenne-type: mental retardation was recorded in 5 of these, the intelligence was said to be normal in 7, and there was no comment about the others. In recent years there has been some controversy about the presence of intellectual impairment in muscular dystrophy. Walton and Nattrass (1954) studied 48 cases of Duchenne-type muscular dystrophy and concluded that, in spite of clinical impressions, no patient was mentally defective and only four were slightly backward. They thought that this clinical impression of backwardness could be attributed to loss of education, or to the reaction of these patients to their physical disability. Truitt (1955) also concluded that the mental ability of a series of patients with pseudohypertrophic muscular dystrophy was 'within the limits of normal expectation for the socio-economic group', that it was commensurate with the intelligence of their sibs, and that it did not decrease with advanced age or progression of the disease. On the basis of the verbal part of the Wechsler Intelligence Scale for children, Morrow and Cohen (1954), in a study of 29 cases, found a mean IQ of 94. Although this was below average, they concluded, on the basis of other psychological data, that the lowered intellectual functioning resulted from the social and educational consequences of the disease and was not a primary consequence of the muscular dystrophy. They also found that in schooling about one-half of the patients were in grades one or more years behind other children of the same age and that 15 out of 23 children over 8 years of age showed reading retardation, while about 50% were retarded in number skills. Del Carlo Giannini and Marcheschi (1959) studied 18 cases of muscular dystrophy, including 7 of the Duchenne-type: 5 of the latter group had a marked reduction in IQ. More recently Allen and Rodgin (1960) found a mean IQ of 82 in a series of 30 boys with muscular dystrophy, ranging in age from 2 to 23 years. Various standard tests were used and the IQ ranged from 14-117. There were 15 boys with an IQ over 95. There was no correlation between the degree of intellectual impairment and the severity of the physical disability. While they also found evidence for depression of intellectual function related to emotional problems associated with the physical handicaps, they did not think this in itself could explain the intellectual impairment. Worden and Vignos (1962) made a detailed study of the intelligence in 38 cases of progressive muscular dystrophy. All but one were over the age of 7. The mean IQ was 83, with a range of 46-134. Only 3 were above 110, while 26 were below 90. There was also evidence of special difficulties with reading and mathematics, and the mean educational quotients in these two fields were 83 and 87 respectively. They found no correlation between the IQ and the disability grading of the disease and no evidence of a progressive mental deterioration with advance of the disease. In a comparative study of 27 unaffected sibs of these patients they obtained a mean IQ of 110 and in a series of 16 cases of 'amyotonia congenita' with equivalent or more severe physical handicap, the mean IQ was 118.