Congenital Myopathies overview
The first report of a congenital myopathy was in 1956, when a patient with central core disease (CCD) was described. Since that time, other myopathies have been defined as congenital myopathies, which have the following characteristics:
- Onset in early life with hypotonia, hyporeflexia, generalized weakness that is more often proximal than distal, and poor muscle bulk
- Often with dysmorphic features that may be secondary to the weakness
- Relatively nonprogressive
- Unique morphological features on histochemical or ultrastructural examination of the muscle biopsy sample that originate within the myofiber
Hypotonia is the clinical hallmark of congenital myopathies. It presents in the neonatal period as head lag; lack of flexion of the hips, knees, and elbows; external rotation of the hips; diffuse weakness in facial, limb, and axial muscles; and reduced muscle mass.
The above features do not apply to all cases of congenital myopathy. Some cases have been reported as adult onset or as a progressive course. Some of the morphological alterations are not disease specific but are seen in various congenital myopathies or in other myopathic or nonmyopathic conditions.
What is Congenital Myopathies?
The congenital myopathies are autosomal dominant inheritable diseases that are evident at or soon after birth.
- Congenital muscular dystrophy (CMD) is evident at birth and causes general muscle weakness and joint deformities. It progresses very slowly and in its severe form (Fukuyama) affects mental function. CMD is caused by a defect of an autosomal dominant gene.
- Central core disease is a slowly progressing skeletal muscle disorder that, unlike most of the muscular dystrophies, is not life-threatening. It is called central core disease because the muscle cells associated with the disease have an abnormal light inner core surrounded by a dark circle. Central core disease develops before early infancy and its symptoms include hip displacement, an inability to jump and run smoothly, and general weakening of the muscles.
- Myotonia congenital, also known as Thomsen’s disease, is a nonprogressive muscle disorder that develops from infancy to childhood. Myotonia is characterized by stiff muscles that take a long time to relax after contraction. It is generally not painful. Unlike many other myopathies, the muscles that are affected (arms, legs, and face) enlarge and do not weaken.
- Paramyotonia congenital, also known as Eulenberg’s disease, is evident at birth, and like myotonia congenita, is characterized by stiff muscles that take a long time to relax after contraction, it is not progressive, and it does not cause muscle weakening. It is triggered by cold temperatures. The hands become clumsy, the face rigid, and the muscles in the forearm stiff.
- Myotubular myopathy, also known as centronuclear myopathy, is a slowly progressive disease that causes drooping of the eyelids, foot drop, facial weakness, and other muscle weakness. It is evident at birth to infancy and is rarely fatal. The weakened muscles usually have no reflexes.
- Nemaline myopathy, also known as Rod body disease, develops from birth to adulthood and is nonprogressive and usually not fatal. Symptoms include weakening of the leg, arm, and trunk muscles and some weakening of various facial and throat muscles. The affected muscles usually have poor reflexes. There is a particularly severe type of nemaline myopathy that, if present at birth, causes death due to breathing complications.
Is there any treatment for Congenital Myopathies?
Currently, only central core disease has an effective treatment (see above). There are no known cures for any of these disorders. Supportive treatment may involve orthopedic treatments, as well as physical, occupational or speech therapy.
What is the prognosis for Congenital Myopathies?
When breathing difficulties are severe, and particularly if there is also a problem with feeding and swallowing, infants may die of respiratory failure or complications such as pneumonia. Sometimes muscle weakness can lead to skeletal problems, such as scoliosis, reduced mobility of joints, or hip problems. The heart muscle is rarely involved.