myopathies and Myasthenias -Neurology/IM Flashcards
Causes of myopathy
A- Inherited (progressive muscular dystrophies):usually present in infancy or adulthood
B- Acquired: usually present in adulthood
1) Endocrinal: Thyrotoxicosis, acromegaly, and Cushing’s syndrome.
2) Carcinomatous: Bronchogenic carcinoma, ovarian tumors.
3) Metabolic: Periodic paralysis syndromes due to disturbance of K balance.
4) Iatrogenic: Corticosteroids, chloroquine, and vincristine.
5) Toxic: Alcohol.
Symptoms of myopathy
1) Clumsy gait.
2) Inability to climb the stairs.
3) Protuberant abdomen.
4) Weakness and wasting of certain muscles
result of weakness and wasting of the shoulder, pelvic girdle and trunk muscles
a) Winging of the scapulae due to weakness of the serratus anterior and trapezius.
b) Pot-belly abdomen due to weakness of the abdominal muscles.
c) Exaggerated lumbar lordosis due to weakness of the extensor muscles of the trunk in an attempt from the patient, to prevent himself from falling forwards by the effect of gravity.
d)Waddling gait due to weakness of gluteus medius and minimums (abductors of the hip).
e) Characteristic manner in getting up from the floor (climbing test or Gower’s sign patient climbing himself) due to weakness of the gluteus maximus.
Investigations of myopathy
1) The serum creatine kinase (CK) level: elevated due to degeneration of the muscle fibers.
▪ In DMD is markedly elevated (as much as 50-100 times normal, or greater).
▪ In BMD (elevated but not as DMD).
2) EMG: Diminished amplitude and duration of motor units, and early interference pattern (myopathic features) this finding is common with all myopathies
3) Ultrasonography: relatively noninvasive technique that is used for screening patients with MD.
4) Genetic testing: demonstrates the level of dystrophin (absent in DMD, ↓↓ in BMD).
5) Muscle biopsy: degeneration of muscle fibers and its replacement by fibrous and fatty tissue.
6) ECG: to detect cardiac affection (80% of cases).
what is the myotonic phenomenon
▪ Improves by: repetition of movement, warmth, calcium, quinine, and procainamide.
▪ Worsened by: cold, potassium and prostigmine.
Pathophysiology of myasthenia gravis
● Thymus gland is abnormal in 75% of patients: hyperplasia (85%) and thymoma (15%).
● AChR antibody production within the thymus gland → target postsynaptic AChRs of normal muscle cells, competing with acetylcholine (ACh) leads to impaired transmission at the NMJ.
