Computational Intelligence in Analysis of Electromyography Signals - Computational Intelligence in Biomedical Engineering - page 229

muscles to waste away due to the lack of a protein called dystrophin that func-
tions to preserve the integrity of muscle cells. This disorder is severe and sur-
vival after the age of 30 is rare. Becker muscular dystrophy (BMD) disorder is
similar to DMD except that onset is in the adolescence. It eventually spreads to
the heart muscle potentially leading to heart failure. Emery-Dreifuss muscular
dystrophy (EDMD) is a slowly progressing disease caused by gene mutations,
which result in defects of emerin, lamin A, or lamin C proteins in the mem-
brane surrounding the muscle cell nucleus. It occurs in children and results
in weakness and wasting of the upper body. Myotonic muscular dystrophy
(MMD) or Steinert's disease can occur in early adulthood but is not as severe
as its congenital form. This is due to a gene defect associated with repeated
sections of DNA on either chromosome 3 or chromosome 19. The disease pro-
gression is slow beginning with weakness in the facial muscles and spreading
throughout the body. Distal muscular dystrophy (DD) is also due to gene
mutation and affects young to middle-aged adults where muscles in the leg
tend to degenerate but the disease is not life threatening. Another gene muta-
tion disorder is limb-girdle muscular dystrophy (LGMD), which affects the
waist and lower limbs. The disease is slowly progressive causing wasting of
the limbs and some cardiopulmonary complications. Other similar disorders
caused by genetic deficiencies or mutations include facioscapulohumeral mus-
cular dystrophy and oculopharyngeal muscular dystrophy (OPMD), which
affects the face and eyes.
5.3.5 Neuromuscular Junction Disorders
The NMJ acts as an interface for transferring electrical nerve impulse to
impulses in the muscle itself. Diseases of the NMJ usually disrupt the recep-
tor interaction and inhibit the function of the neurotransmitter acetylcholine.
EMG readings show distinct instability of the MUAP waveform (jitter) where
no two successive waveforms are exactly the same (Hassoun et al., 1994).
This characteristic is due to instability in the damaged NMJ and can be best
detected by single-fiber electromyography (SFEMG).
There are several variants of NMJ disorders, each with a different manifes-
tation. Myasthenia gravis (MG) is an autoimmune disorder where the body's
immune system attacks the NMJ area targeting the acetylcholine receptor
or muscle-specific kinase, which helps organize acetylcholine receptors on the
muscle cell membrane. The etiology of the disorder is unclear although some
theories of bacteria or viruses as being likely causes exist. The disease seems
to affect women more than men causing weakness or tiredness in voluntary
muscles. A similar disorder is Lambert-Eaton myasthenic syndrome (LES)
associated with weakness in the lower limbs with about 60% of the cases
accompanied by cancer. Congenital myasthenic syndrome (CMS) presents
prior to birth causing defects in the genes necessary to produce the required
NMJ proteins. Symptoms and prognosis vary depending on the severity of the
disorder because problems could occur with the presynaptic and postsynaptic