• It is a chronic disorder in NMJ
characterized by easy muscle
fatiguability on repetition of
movement & relieved by rest.
• It is due to impairment of conduction at the
1- Acetyl choline deficiency.
2- Choline esterase in excess.
3- Curare- like substance at the N.M.J.
increasing the threshold of motor end plate to
Acetyl Choline . the thymus gland is blamed for
secretion of such substance.
4- Recently the disease is considered as an
auto-immune disorder, antibodies against A.ch
receptors in NMJ.
* Most characteristic feature is Easy Fatiguability on
repetition of movement.
• Characteristic descending march course:
A) Ocular: ptosis is the earliest symptom. Later
ophthalmoplegia & diplopia. pupillary reaction are normal.
B) Facial: expressionless (mask face). On smiling
C) Jaw muscles: mouth hanging open.
D) Bulbar: dysarthria, dysphagia, nasal regurgitation & nasal
tone of voice.
E) Other muscles: neck muscles (head lolling), upper limbs
more than lower limbs (prox. > distal), respiratory muscles
leading to dyspnea.
* Diurnal variation:
After night rest the patient wakes up in the
morning nearly normal but as the day goes on
with its activity the muscle gradually become
* Tendon reflexes: normal but after repeated
tapping lost .
* Muscles atrophy: may occur in long standing
* Some cases may be associated with
thyrotoxicosis or enlarged thymus gland .
1- Clinically: a ) The descending march character
and the diurnal variation.
b) Induction of fatigue by repetition of
c) Walker's test: sphygmomanometer is
applied to the arm. The pressure is raised above
the systolic. The patient is asked to do rapid
repetitive movements with his hand till exhaustion
occurs. The cuff is then released. In case of
myasthenia ptosis will occur within a few
2- Pharmacological tests:
a) Prostigmine test : I.M injections of 2.5 mg
prostigmine + one ampoule atropine ( to
counteract the action of prostigmine on the
smooth muscles of intestine), improvement
occurs within 1/2 h in myasthenia.
b) Tensilon test: 8 mg I.V improvement occurs
within 1 min.
Reduction in amplitude of the motor action
potentials on successive motor activity
4) CT & Plain X-ray
chest may show thymic enlargement.
5) Serological tests:
Anti-AchR Ab in serum of 85-90% pt.
N.B. seronegative myasthenia gravis refers to
disease without detectable (anti-AChR) Ab. In
these patients, IgG antibodies against the musclespecific kinase (MuSK) have been described.
6) Muscle biopsy:
1 ) Rest: avoid excessive exercise and
2 ) Medical:
I) Anticholinesterase drugs:
II) Steroids: Prednisolone in pt. not
responding to I) may give remission up to 5
III) Other immunosuppressant drugs: e.g.
Azathioprine in pt. not responding to
3) Plasmapharesis: Pt.’s plasma exchanged for
albumin to reduce AchR ab level. Repeated every
a) Thymectomy: May be needed in severe cases
especially in young patient with duration less
than 3 years . the prognosis is better if no
thymoma. In pt. with thymoma irradiation should
be tried before operation .
b) Thyroidectomy: If there is associated
Easy fatiguability secondary to known diseases:
1) Bronchogenic carcinoma.
3) Lupus erythematosis.
• In this condition there:
- No descending march.
- Not responding to prostigmine but to guanidine
- E.M.G after repetitive movement increase
amplitude of motor action potential (incrementing
response). Eaton- Lambert phenomenon.
Myasthenic women's infants show
myasthenic manifestations at birth.
• Due to transplacental passage of AchR
• Poor crying, suckling & floppy infant.
• They recover spontaneously within 2 –
• We may use Anticholinesterase drugs.
* Very rare.
* Starts in infancy.
* Structural abnormality in the
AchR at NMJ.
* persists for life.
* No treatment.
• Crisis in myasthenia : It is of two types :
1 ) Myasthenic crisis : due to increase of the
severity of myasthenia with sudden deterioration in
2) Cholinergic crisis : due to over dosage in ttt
(choline esterase intoxication ).
I) weakness of the muscles which simulate
myasthenic crisis .
II) Fasciculations , pallor , sweating , small pupils
and excessive salivation.