numerous forms of myopathy, many of which are
congenital (present at birth) or genetic (the result
of inherited GENEmutations). Some myopathies
are progressive (become worse with time) and
others remain stable. Metabolic disorders, HIV/AIDS,
IMMUNE DISORDERS, and ADVERSE REACTIONto drugs
(including ALCOHOL) may cause myopathies. Treat-
ment targets the cause of the myopathy in
acquired myopathy and attempts to relieve symp-
toms when myopathy is congenital or genetic.
Treatment approaches may include medications,
PHYSICAL THERAPY, braces or other devices to sup-
port weak muscle structures and aid mobility, and
MASSAGE THERAPY.
See also CARDIOMYOPATHY; GENETIC DISORDERS;
INHERITANCE PATTERN; MITOCHONDRIAL DISORDERS;
MUTATION; NEUROPATHY; POLYMYOSITIS.
myotonia A neuromuscular circumstance in
which the muscles contract properly but do not
relax, causing temporary stiffness. Movement may
be slow and difficult until the muscles warm up,
after which they seem to function more smoothly.
Myotonia may be a symptom, such as with some
forms of MUSCULAR DYSTROPHY, or a congenital con-
dition. Myotonia congenita is a rare form of
myotonia that occurs as a result of GENEmuta-
tions. Some forms of myotonia are progressive
though most are not. Myotonia is a disorder of the
ion channels in the MUSCLEcells (channelopathy),
most often the chloride, sodium, or potassium
channels. The ion channels regulate the ion
exchange that must occur for a cell to “fire,”
which in the case of muscle cells is to contract and
relax.
The diagnosis of myotonia is primarily clinical,
based on the doctor’s observance of the person’s
movement and muscle function. Characteristic
alterations in the electromyogram (EMG) gener-
ally can confirm the diagnosis. Treatment with
antiseizure medications and drugs that affect the
ion channels often improve symptoms and muscle
function. Myotonia resulting from another disor-
der often improves when the underlying condi-
tion improves. Though myotonia is a lifelong cir-
cumstance, most people who have myotonia are
able to enjoy fairly normal lifestyles with appro-
priate medication therapy.
See also CELL STRUCTURE AND FUNCTION; GENETIC
DISORDERS; INHERITANCE PATTERN; MUTATION; MYOPATHY;
NEURON.neurogenic arthropathy Degeneration of a JOINT,
commonly the knee, as a consequence of NEUROPA-
THY(impaired NERVEfunction) that causes loss of
sensation. Injuries occur to the affected joint
because there is limited perception of PAINor sense
of the joint’s position relative to the body and its
immediate environment (PROPRIOCEPTION). Neuro-
genic arthropathy sometimes called Charcot’s
joints, often includes unrecognized fractures that
do not heal properly because the joint is in contin-
uous motion. As a result the joint becomes
deformed and dysfunctional, changes that cause
only mild discomfort because of the underlying
NEUROPATHY.
The diagnostic path begins with recognition of
the underlying neuropathy. X-RAY can usually
confirm the damage to the joint. Treatment for
neurogenic arthropathy aims to preserve joint
structure and function to the extent possible and
may include BONEgraft or surgery to stabilize the
joint. Some people are good candidates for JOINT
REPLACEMENT, though in progressive forms of neu-
rogenic arthropathy the joint may continue to
deteriorate around the prosthesis.CONDITIONS ASSOCIATED
WITH NEUROGENIC ARTHROPATHY
AMYLOIDOSIS CHARCOT-MARIE-TOOTH(CMT)DISEASE
DIABETES Hansen’s disease (leprosy)
SPINA BIFIDA SPINAL CORD INJURYSee also CHARCOT-MARIE-TOOTH(CMT) DISEASE;
FRACTURE; INFECTIOUS ARTHRITIS; OSTEOARTHRITIS;
RHEUMATOID ARTHRITIS.340 The Musculoskeletal System