A myopathy is a disorder of the muscles that usually results in weakness. Congenital myopathy refers to a group of muscle disorders that appear at birth or in infancy. Typically, an infant with a congenital myopathy will be "floppy," have difficulty breathing or feeding, and will lag behind other babies in meeting normal developmental milestones such as turning over or sitting up.
No specific treatment is available for any of the congenital myopathies, but aggressive supportive care is essential to preserve muscle activity, to allow for maximal functional ability, and to prolong life expectancy. The primary concerns affecting prognosis are preventing and correcting skeletal abnormalities (eg, scoliosis, foot deformities, contractures) to maintain ambulation, and to prevent or delay the development of respiratory insufficiency. Respiratory failure due to diaphragmatic weakness can occur at any age and may be independent of the degree of limb weakness. A restrictive pattern on pulmonary function tests (PFTs) may be apparent before the onset of symptoms. Early symptoms of nocturnal hypoxia can include poor sleep, nightmares, morning headache, daytime sleepiness, and weight loss. All patients should have baseline PFTs that are repeated in at least yearly intervals. Treatment options include chest physiotherapy, manually assisted cough, early treatment of respiratory infections, noninvasive ventilation, and tracheostomy combined with permanent ventilation.
No lesions are seen in peripheral nerves, and the condition is thought to involve excessive activity of the neuromuscular spindle reflex arc. Adult cattle are affected at 3–7 yr of age. Extensor muscles of the back and pelvic limbs are affected, causing lumbar lordosis and caudal extension of the limbs. This condition is also thought to be familial and is usually progressive. Mephenesin (30–40 mg/kg, PO, for 2–3 days) may produce variable control of signs. Quadriceps muscle hypoplasia as a cause of congenital lameness has been described in Holstein calves. Reduced numbers of spinal cord motor neurons suggest that there is failure to innervate the muscle on the affected side.