NMJ Disorders Flashcards
Myasthenia Gravis
What are the two variants of the disease?
Ocular MG (10-20%)
Generalized MG (80-90%)
Myasthenia Gravis
Clinical Signs and Symptoms
Ocular– ptosis, diplopia
Generalized–ptosis, diplopia, dysarthria, dysphagia, respiratory, facial, neck, limb weakness
PRESERVED sensation and reflexes
What causes MG?
Autoantibodies form against the Ach receptor
Loss of functional AchR leads to weakness
Myasthenia Gravis
How does the NMJ appear in this disease?
Lose the folds of the muscle due to loss of AchR
Myasthenia Gravis
What diagnostic tests may be performed?
Tensilon (Edrophonium) test – give an acetylcholinesterase inhibitor to see if there is short-term symptom improvement
EMG evidence can indicate abnormal NMJ transmission
Elevated serum Ab titer against AchR
Myasthenia Gravis
Treatment
Acetylcholinesterase inhibitors may be used to improve symptoms
Thymectomy
Immunosuppressant drugs– corticosteroids, cyclosporine, azathioprine, mycophenolate mofetil, plasmapharesis or IVIG
Why is a thymectomy considered in the treatment of MG?
Thymus contains AchR-like material, which could be where the autoimmune response is initiated?
Lambert-Eaton Myasthenic Syndrome (LEMS)
Clinical Signs and Symptoms
Fatiguable weakness of proximal limbs, trunk (mimicking a myopathy)
Hyporeflexia
Dry mouth
Orthostasis
Lambert-Eaton Myasthenic Syndrome (LEMS)
What is the cause?
Autoantibodies formed against presynaptic Ca2+ channels
Lambert-Eaton Myasthenic Syndrome (LEMS)
What disease is it often related to?
Small Cell Lung Cancer
Lambert-Eaton Myasthenic Syndrome (LEMS)
How is it diagnosed?
Nerve stimulation tests
EMG
Sometimes detect specific antibodies
Lambert-Eaton Myasthenic Syndrome (LEMS)
Treatment
Find and treat underlying cancer
Drugs to enhance Ach release– guanidine or 3,4 diaminopyridine
Immunosuppressive therapy
