Listed below are some of the specific types of myopathies. Most myopathies present in similar ways, but there are some differences within the types. The similarity in presentation, however, is why a muscle biopsy is necessary for a specific diagnosis. This list is not all-inclusive, as there are differences in opinions as to what constitutes a symptom and what a diagnosis. Researchers have also found myopathic changes on biopsies which have not been associated with any known myopathy. I have tried to include here the generally accepted congenital myopathies.
Myotubular Myopathy · Congenital Fiber-Type Disproportion
Central Core Disease was one of the first congenital myopathies to be documented. It is characterized by the presence of "central cores" within the muscle. This disorder is further discussed on the Central Core Disease page.
This myopathy is also called Minicore Disease, Multicore Disease, Minicore Myopathy, Multicore Myopathy, or Multicore/Minicore Myopathy. It is one of the more recently documented myopathies. It generally presents with mild, usually non-progressive (or slowly progressive) weakness. There may be associated heart problems due to weakness of the heart muscles. Weakness of the chest muscles can cause difficulty in night breathing. The muscle weakness tends to be more proximal than distal, and there is sometimes facial weakness. Some individuals report pain, but others do not. Upon muscle biopsy, cores are present in the muscles, but are differentiated from those found in Central Core Disease by their shape, which is oval. As with all myopathies, the degree of weakness may vary greatly from one person to another.
Nemaline Myopathy is sometimes called Nemaline Rod Myopathy because of the thread-like structures found in the muscle. As with the other myopathies, nemaline often presents with muscle weakness and delayed motor milestones. There may be heart and repiratory involvement. Some people may have benign, non- or slowly-progressive weakness, and others can have more extensive involvement. In infants with respiratory weakness, early diagnosis and ventilation can help the child over early difficulties and improve prognoses. There is a severe variant of nemaline myopathy with what appears to be a slightly different inheritance. This variant presents with extreme weakness at birth and an often fatal outcome. Nemaline myopathy appears to have a greater range of severity than some of the other myopathies.
Also known as Centronuclear Myopathy, myotubular myopathy is so called because parts of the muscle resemble the "myotubes" of fetal muscle. Researchers speculate that the muscle development may be arrested in these individuals, but this has not been proven. Like the other myopathies, myotubular myopathy often presents in infancy or early childhood with muscle weakness. There may be weakness of the eye and facial muscles. As with the other myopathies, the degree of weakness varies. The disorder is often non-progressive or only slowly progressive. Severe X-linked Myotubular Myopathy is a variant. Infants with the X-linked condition have severe hypotonia and muscle weakness, respiratory involvement, and difficulty in swallowing. This variant is sometimes fatal.
On muscle biopsy, persons with congential fiber-type disproportion show smaller type 1 fibers than type 2. In normal muscle, the two types are of equal size. There is some disagreement as to whether CFTD is a myopathy, or a symptom of an unknown disorder. CFTD presents with moderate weakness in infancy or early childhood. Respiratory problems are often associated with CFTD, as are congenital dislocations of the hip. Children with CFTD are often small for their age. There can appear to be a slight progression of the disorder in the first year of life, but once children reach the age of two, they generally remain static or progress. As compared to individuals with other non- or slowly-progessive myopathies, those with CTFD seem to have more symptomatic involvement in infancy.
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