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Neuromuscular diseases
Definition
• muscle function disorder
• caused by defect of muscles and/or nervous control
Classification
• myopathies (muscle dystrophy)
• neural atrophy (primary peripheral nerve damage, secondary muscle
athrophia)
• basal ganglia atrophy
• motor end plate diseases (Myasthenia gravis)
Myasthenia gravis
Definition
• Autoimmune disease leading to fluctuating muscle weakness and
fatigability caused by circulating antibodies that block acetylcholine
receptors in the postsynaptic part of neuromuscular junction
• the autoantibodies against nicotinic acetylcholine receptor on the
postsynaptic membrane of the motor end plate
– inability of acetylcholine to bind to receptor
– destruction of receptors
Causes:
• unknown
• genetic predisposition? – HLA (B8, DR3, DR1)
• abnormality of the thymus (75% of patients)
Classification
(Myasthenia Gravis Foundation of America Clinical Classification)
• Class I: Any eye muscle weakness, possible ptosis, no other muscle
weakness elsewhere
• Class II: Eye muscle weakness of any severity, mild weakness of other
muscles
– Class IIa: Predominantly limb and axial muscles
– Class IIb: Predominantly bulbar and/or respiratory muscles
• Class III: Eye muscle weakness of any severity, moderate weakness of
other muscles
– Class IIIa: Predominantly limb and axial muscles
– Class IIIb: Predominantly bulbar and/or respiratory muscles
• Class IV: Eye muscle weakness of any severity, severe weakness of
other muscles
– Class IVa: Predominantly limb and axial muscles
– Class IVb: Predominantly bulbar and/or respiratory muscles (feeding tube,
without ventilation)
• Class V: Intubation needed to maintain airway
Neuromuscular junction
Signs and symptoms
• fatigability – muscles become progressively weaker during activity and
improve after rest – myashenic reaction
• especially facial muscles – muscles that control eye and eyelid
movement, facial expression, chewing, talking, swallowing – facies
myasthenica
– ptosis (dropping of eyelids)
– diplopia (double vision)
– dysphagia (difficulty in swallowing)
– dysarthria ( impaired speech)
• also affected muscles control breathing and neck and limb movement
– shortness of breath
– waddling gait
– weakness in arms, hands, fingers, legs, neck
• other physical examination – in normal limits
Regional distribution of
muscle weakness
95%
60%
30%
10%
Ptosis and weakness of smile
Improvement after therapy
In early stages patient may feel fine
in the morning but develops diplopia
and speech slurs later in the day
Patient with chin on chest cannot resist
when physician pushes head back
Blepharoptosis of the left eye
Weakness of neck
Lambert-Eaton myasthenic
syndrome
Definition
• Autoimmune disease lthat affects voltage-gated calcium channels on
the presynaptic membrane of the neuromuscular junction, that leads to
inhibition of acetylcholine release from the presynaptic terminal
Causes:
• small-cell lung cancer (50%)
• genetic predisposition?
Signs and symptoms
• progressive weakness (not involve/or rare facial and respiratory
muscles)
• the symptoms are worse in the morning and improve with excercise
(opposite to MG)
• predominantly affected proximal parts of legs and arms
• autonomic symptoms – dry mouths, impotence
• reduced or absent reflexes
Areflexia
Difficulty in climbing stairs or
arising from chair often early
symptom due to weakness of
muscles
Dryness of mouth due to
decreased saliva secretion
Mucular dystrophy
Definition
• Group of hereditary muscle diseases characterized by progressive
skeletal muscle weakness
Causes:
• inherited (XR)
Signs and symptoms
• progressive muscular weakness
• poor balance
• walking difficulty, frequent falls, inability to walk
• calf pain
• limited range of movement
• dropping eyelids
• scoliosis
Duchenne muscular dystrophy
Definition
• Inherited muscular dystrophy characterized by rapid progression of muscle
degeneration, eventually leading to loss of ambulation and death.
Causes:
• X recessive inherited mutation of DMD gene (Xp21) that codes the protein
dystrophin – structural component of muscles - no protein production
Signs and symptoms
• progressive muscle weakness – pelvis, calves, arms, neck (age 5-6 years)
• awkward manner of walking, running (on forefoot)
• frequent falls
• fatigue
• lumbar lordosis, scoliosis
• muscle contractures
• pseudohypertrophy of tongue and calf muscles
• higher risk of learning dificulties (because of muscular fatigue)
Becker´s muscular dystrophy
Definition
• Inherited muscular dystrophy characterized by slowly progressive muscle
weakness of legs and pelvis
Causes:
• X recessive inherited mutation of DMD gene (Xp21) that codes the protein
dystrophin - lower concentration of dystrophin
Signs and symptoms
• slowly progressive muscle weakness (sometimes normal walking into
adulthood, variable)
• toe-walking
• frequent falls
• difficulty breathing
• skeletal deformities