Contributory etiologic factor for talipes equinovarus in congenital myotonic dystrophy: comparative biopsy study of intrinsic foot musculature and vastus lateralis in two cases

Orthopaedic manifestations of congenital myotonic dystrophy during childhood and adolescence

BACKGROUND

Congenital myotonic dystrophy (CMD) is a dominantly inherited disorder manifested in childhood by muscle weakness which can be profound at birth, but which progressively improves over the first few years. Congenital myotonic dystrophy represents the severe end of the spectrum of myotonic dystrophy, which in milder cases may not be diagnosed until adulthood. The goal of the study was to identify and quantitate the musculoskeletal deformities which may significantly affect the function of children with CMD.

METHODS

A retrospective chart and radiograph review was performed after Institutional Review Board approval for all cases of myotonic dystrophy from 1987 to 2004 followed at a children's specialty orthopaedic hospital. Inclusion criteria were either a conclusive testing for CMD by gene testing, electromyography, and/or muscle biopsy in the child or parent and the presence of a typical clinical picture. Skeletal manifestations were classified by body segment (upper extremity, hand, spine, hip, lower extremity, foot) and by the type of deformity. Surgical procedures and outcomes were also documented.

RESULTS

Thirty children and adolescents met the inclusion criteria. The male/female ratio was 1 (15 boys and 15 girls). In 27 cases, the mother transmitted the disease, and in 2 cases, the father transmitted the disease; in one case, it was impossible to reconstitute the family history of the child who was adopted. The mean age at onset of gait was 29 months. Twenty-two (73%) out of 30 children underwent surgery for lower extremity-, foot-, or spinal-related deformities. The mean follow-up was 11.4 years (range, 3-20 years).No contractures or deformities were observed in the upper extremities. Spinal deformities affected 9 patients (30%), and 3 of these required surgery. These spinal deformities when present usually had an early onset and included thoracolumbar scoliosis as well as kyphoscoliosis. Problems at the level of the hips and knee were infrequent and included only 2 patients who had unilateral hip abduction contracture and 1 patient who had significant fixed knee flexion contracture. Congenital clubfoot occurred in 5 patients (17%) and generally responded well after posteromedial release and recurrence occurred in only one case. Developmental equinus and equinovarus exclusive of clubfoot affected 7 patients (23%), 70% of whom required surgery. Outcome after Achilles tendon lengthening was positive, and many of the children began walking soon after the Achilles lengthening, and recurrence did not occur.

CONCLUSIONS

Child with CMD are at high risk for musculoskeletal deformities of the spine and lower extremities. In our experience, correction and improved function were likely after surgery.

LEVEL OF EVIDENCE

Retrospective study; level IV.

Histologic and histochemical analysis of muscle specimens in idiopathic talipes equinovarus

Congenital idiopathic talipes equinovarus is a relatively common disorder of uncertain etiology with a wide variance of clinical severity. Many theories have been postulated over the years without universal agreement in regard to the cause of this disorder. These hypotheses include vascular, viral, genetic, anatomic, compartment syndrome, environmental, and positioning considerations. A great deal of recent discussion has focused on a neuromuscular etiology for this condition. Muscle biopsies from the gastrocnemius, abductor hallucis, flexor digitorum longus, flexor hallucis, and tibialis posterior were obtained during posteromedial surgical release for idiopathic talipes equinovarus from September 1994 to October 2000 at the authors' institution. Ninety-five feet in 68 patients yielded a total of 431 muscle specimens. All of the specimens were processed and examined by light microscopy by an expert neuromuscular pathologist. In addition, 95 tissue samples were further processed for histochemical studies and electron microscopy. Three hundred seventy-two specimens (86.3%) showed no evidence of a pathologic diagnosis with normal fiber-type ratios and no type I fiber grouping indicative of neuromuscular pathology. Only 4 specimens (0.9%) showed type I fiber predominance, and 55 specimens (12.8%) revealed muscle fiber atrophy. The results of this study do not support the theory that a neuromuscular abnormality may be significant in the etiology of idiopathic talipes equinovarus.

Presentation, clinical course, and outcome of the congenital form of myotonic dystrophy

We report the clinical experience of 18 patients with the congenital form of myotonic dystrophy, the majority of whom were diagnosed during the neonatal period and monitored from 5 to 14 years. Prematurity associated with congenital myotonic dystrophy gives rise to the severest clinical manifestations. Among them, respiratory involvement is common and is the leading cause of death in the neonatal period. Weakness and foot deformities secondary to muscle involvement are the predominant clinical features of this group of patients from birth to age 3 or 4 years. Once muscle strength improves, learning disabilities and behavioral disturbances become the main clinical problems. All our patients, when tested after 5 years of age, had intelligence quotients under 65, clearly below the average intelligence quotient of their mothers (IQ = 80). There is no relationship between the degree of mothers' and patients' disease. No patient has presented problems with routine immunizations, and no complications were observed in the 7 patients who underwent surgery under general anesthesia. Among the surviving patients, no correlation can be established between severity of disease in the neonatal period and the magnitude of sequelae as teenagers. Mental and behavioral disturbances are the factors which mainly influence the long-term management and prognosis of this cohort of individuals.

Myotonic dystrophy

Myotonic dystrophy (MYD) has been localized to chromosome 19. Like other hereditary diseases with a genetic locus assigned to chromosome 19, MYD is a genetically inherited autosomal dominant disease. It is speculated that such a genetic pattern may express the characteristics of chromosome 19. We previously proposed that abnormalities of bile acid metabolism play a pathogenetic role in MYD, in which deoxycholic acid acts as a maternal factor in association with the onset of congenital MYD. Increased gamma-glutamyl-transpeptidase (gamma GTP) (probably hydrophobic deoxycholate-solubilized gamma GTP instead of hydrophilic papain-solubilized gamma GTP) in MYD may be related to the abnormalities of bile acid metabolism. Muscle wasting in MYD may be explained by these abnormalities as well. The resemblances between common metabolism of bile acids and alcohol and between common changes in MYD and alcoholic myopathy may lend support to a hypothesis that 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha, 26-tetrol dehydrogenase and 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestan-26-al dehydrogenase activities are impaired in MYD.