Orthopaedic Surgery
Other Myopathies
Myopathies classify a group of diseases that affect skeletal muscles, muscles connected to the bones. Almost all myopathies cause weakening and gradual wasting of the muscles, especially those closest to the center of the body. Myopathies can be caused by inherited genetic defects (i.e., muscular dystrophies), and endocrine, inflammatory (i.e., polymyositis), and metabolic disorders. Some myopathies develop at an early age; others develop later in life.
Myotonia Congenita (MC) (two forms: Thomsen's and Becker's Disease)Myotonia Congenita is an autosomal recessive genetic, neuromuscular disorder characterized by the slow relaxation of the muscles. The disorder is caused by mutations in a gene that carries instructions for a chloride channel, a pore in the muscle cell surface that regulates the movement of chloride molecules. Symptoms may include delayed muscle relaxation and muscle stiffness, which usually are provoked by sudden movements after rest. The disease is diagnosed usually anywhere from early to late childhood.
Paramyotonia Congenita (PC)Paramyotonia Congenita is an autosomal dominant genetic, neuromuscular disorder usually diagnosed at or near birth. The disease is caused by mutations in the gene that carries instructions for a sodium channel, a pore in the muscle cell surface that regulates the movement of sodium molecules. PC causes problems with tone and contraction of skeletal muscles; symptoms may include muscle stiffness and weakness (mostly in the face, neck and upper extremities).
Central Core Disease (CCD)Central Core Disease (CCD) is one of a group of diseases that cause problems with tone and contraction of skeletal muscles. Usually diagnosed at or near birth, CCD patients usually suffer from poor muscle tone and persistent muscle weakness and motor milestones are reached late. Skeletal deformities, including joint dislocation and scoliosis, often occur as well. Autosomal inheritance results in a defective gene that carries instructions for a molecular "gate" that releases calcium from inside muscle cells.
Nemaline Myopathy (NM)Nemaline Myopathy is a neuromuscular disorder characterized by muscle weakness and the presence of nemaline bodies in the muscle fibers. NM has two forms, one autosomal recessive and one autosomal dominant. Muscle weakness is usually most severe in the face, the neck flexors and the proximal limb muscles. Patients often suffer from respiratory problems and infants commonly have problems with feeding. NM is usually diagnosed by infancy, however, childhood-onset and adult-onset cases have been identified.
Myotubular Myopathy (MTM or MM)Myotubular Myopathy (MM) characterizes a group of disorders that cause problems with the tone and contraction of skeletal muscles. The most common and congenital form is X-linked, meaning it is carried on the X chromosome and usually affects only boys. This form is caused by defects or deficiencies of myotubularin, a protein thought to promote normal muscle development. Patients usually suffer from severe muscle weakness and hypotonia (lack of muscle tone). This results in a patient's inability to have proper posture and movement. X-linked MM patients also have life-threatening difficulties with feeding and respiration. Anemia and serious liver abnormalities are also not uncommon. The autosomal dominant form onsets anywhere from childhood to adulthood and the autosomal recessive form onsets from infancy to early adulthood. Both autosomal forms cause similar problems to X-linked, but the autosomal dominant form is considered mild, and the autosomal recessive form is considered intermediate. Both types affect the child's ability to attain motor milestones at normal times. In autosomal forms, muscle problems are progressive.
Periodic Paralysis (PP) (two forms: Hypokalemic-HYPOP- and Hyperkalemic-HYPP)
Periodic Paralysis are rare disorders of the voluntary muscles characterized by episodes of attacks or muscle weakness. Between these attacks, affected muscles most often work normally. There are two forms of PP: Hypokalemic and Hyperkalemic. In hypokalemic, low levels of potassium in the blood interact in an unknown way with genetically caused abnormalities in calcium changes in muscle cells. In hyperkalemic, high levels of potassium in the blood interact in an unknown way with genetically caused abnormalities in sodium channels in muscle cells. Each condition is also sometimes caused by genetic abnormalities in channels for sodium or potassium. Both forms are inherited by a defective gene contributed by one parent (autosomal dominant). Hyperkalemic is diagnosed during childhood, whereas hypokalemic can onset anywhere form childhood to adulthood. In hyperkalemic, the frequency of attacks declines after middle age. The number of attacks with hypokalemic patients usually varies, but severe attacks cause nearly full-blown paralysis.
