Practice Essentials
Muscular dystrophy (MD) is a collective group of inherited noninflammatory but progressive muscle disorders without a central or peripheral nerve abnormality. The disease affects the muscles with definite fiber degeneration but without evidence of morphologic aberrations.
The first historical account of MD was reported by Conte and Gioja in 1836.
They described two brothers with progressive weakness starting at age 10 years. These boys later developed generalized weakness and hypertrophy of multiple muscle groups, which are now known to be characteristic of the milder Becker MD. At the time, however, many thought that Conte and Gioja described tuberculosis; thus, they did not achieve recognition for their discovery.
In 1852, Meryon
reported in vivid details a family with four boys, all of whom were affected by significant muscle changes but had no central nervous system abnormality when examined at necropsy. Meryon subsequently wrote a comprehensive monograph on MD and even went on to suggest that a sarcolemmal defect was at the root of the disorder. He further suspected that the disorder is genetically transmitted through females and affects only males.
Guillaume Duchenne was a French neurologist who was already famous for his application of faradism (the use of electric currents to stimulate muscles and nerves) to the treatment of neurologic disorders when he wrote about his first case of MD.
In 1868, he gave a comprehensive account of 13 patients with the disease, which he called “paralysie musculaire pseudo-hypertrophique.” Because Duchenne was already held in high esteem for his work in faradism and for his contributions to the understanding of muscle diseases, one of the most severe and classic forms of MD, Duchenne MD, now bears his name.
Advances in molecular biology techniques illuminate the genetic basis underlying all MD: defects in the genetic code for dystrophin, a 427-kd skeletal muscle protein (Dp427). These defects result in the various manifestations commonly associated with MD, such as weakness and pseudohypertrophy. Dystrophin can also be found in cardiac smooth muscles and in the brain (accounting for the slight mental retardation associated with this disease).
Minor variations notwithstanding, all types of MD have in common progressive muscle weakness that tends to occur in a proximal-to-distal direction, though there are some rare distal myopathies that cause predominantly distal weakness. The decreasing muscle strength in those who are affected may compromise the patient’s ambulation potential and, eventually, cardiopulmonary function.
In addition, structural soft-tissue contractures and spinal deformities may develop from poor posturing caused by the progressive muscle weakness and imbalance, all of which can further compromise function and longevity. Equinovarus contractures start as flexible dynamic deformities and advance to rigid contractures. This altered anatomy prevents normal ambulation, proper shoe wear, and transfers (how patients can be picked up to transfer out of their chair).
Once wheelchair-bound, patients with MDs tend to develop worsening contractures, osteopenia (initially, followed by osteoporosis), and rapidly progressive scoliosis. The change in bone mineral density (BMD) can lead to fractures of the long bones or vertebrae, which in turn lead to more immobilization, disuse demineralization, and exacerbation of scoliosis. On average, for each 10° of thoracic scoliosis curvature, forced vital capacity (FVC) decreases by 4%.
In a patient with an already weakened cardiopulmonary system, this decrease in FVC could rapidly become fatal.
The goal of orthopedic management is, therefore, to preserve or prolong patients’ ambulatory status for as long as possible. This goal can be achieved with soft-tissue releases for contractures, vigilant monitoring of BMD (especially when the patient is on steroid therapy), and treatment of osteoporosis. If patients develop significant scoliosis, which generally occurs after they stop walking, early stabilization of the spine should be considered.