Minicore myopathy in children: a clinical and histopathological study of 19 cases

Minicore myopathy is a congenital myopathy characterized by multifocal areas of degeneration in muscle fibres. Genetic heterogeneity expected on the basis of clinical variability awaits further resolution. We reviewed 19 cases in order to further delineate the phenotype. Marked hypotonia was the predominant presenting feature, with evidence of antenatal onset in 30% of cases. Weakness was most pronounced axially and proximally, often more severely affecting the shoulder girdle. Mild facial involvement was frequent. Varying degrees of scoliosis were obvious in all patients older than 10 years. In addition, two patients who were also the most severely affected had complete external ophthalmoplegia. One patient showed marked distal involvement. Respiratory failure developed in half of all patients after 10 years of age and correlated strongly with the degree of scoliosis. Cardiac involvement occurred mainly secondary to respiratory impairment. The course appeared static in most cases. Loss of independent walking was observed only in one case at the age of 10 years. On ultrasound scan, differential involvement within the quadriceps was documented in several patients. Variability in fibre size, type 1 predominance and atrophy with occasional type 2 hypertrophy were prominent but nonspecific histological changes. Apart from typical minicores, a marked increase in internal nuclei was the most prominent histological feature. With the exception of one family in which two generations were affected, inheritance appeared autosomal-recessive or sporadic in all cases.