NMJ transmission disorders Flashcards
presynaptic NMJ disorder = reduced ACh release
Lambert-Eaton syndrome
Lambert-Eaton syndrome
small cell lung cancer in 50% patients
Lambert-Eaton syndrome aetiology
rare autoimmune response inhibits Ca2+ channels - so inhibits ACh release
antibodies directed at voltage gated calcium channels
Lambert-Eaton presentation
60yrs = average onset age
Characterized by fatigue, weakness in limb muscle groups, autonomic dysfunction
Abnormal reflexes = Areflexia
Does not usually effect respiratory, facial or eye muscles.
Dry mouth = Xerostomia
Symptoms almost always precede detection of cancer - patients rarely complain of lung issues
Lambert-Eaton syndrome diagnosis
Electromyography (EMG) – apply electrical impulses to nerves and measuring the electrical response of the muscle
= Compound muscle Action Potential (CMAP)
chest X-ray - lung cancer
Lambert-Eaton syndrome treatment
Underlying malignancy treat
Use of immunosuppressant’s such as corticosteroids
Amifampridine
Amifampridine
drug which blocks K+ channel so action potential duration is increased, so more ACh released
postsynaptic NMJ disorder - reduced nAChR activation
Myasthenia Gravis (from Greek meaning muscle weakness)
Myasthenia Gravis cause
autoimmune response against nAChR’s – NMJ less responsive to Ach
Myasthenia Gravis = bimodal distribution
20s and 60s years
Myasthenia Gravis comlications
women = hyperplasia of thymus (younger)
men = thymoma (older)
hyperplasia
gross enlargement
thymoma
cancer of thymus
Myasthenia Gravis diagnosis
Edrophonium or neostigmine test
MRI/CT scan for thymoma
Myasthenia Gravis treatment
Directed at enhancing transmission (anticholinesterase)
= edrophonium or neostigmine
Immunosuppresion (corticosteroids)
