Neuromuscular Junction Disorders

Info

🌱 來自: Huppert’s Notes

Neuromuscular Junction Disorders🚧 施工中

Neuromuscular Junction Disorders

Exam is notable for LMN signs which are usually symmetric; may have proximal muscle weakness; check for bulbar signs/symptoms (“D” symptoms – Dysphagia, Diplopia, Dysarthria); may have extraocular movement restriction, ptosis and shortness of breath (especially orthopnea). No fasciculations or atrophy because there is no denervation.

Myasthenia gravis

•   Pathophysiology: Autoantibodies against the Ach receptor on the post-synaptic membrane

•   Symptoms: Weakness after extended muscle use (e.g., worse with use, improves with rest). Can involve ocular muscles (causing ptosis, diplopia) or bulbar muscles (causing dysarthria, dysphagia). Respiratory weakness = myasthenic crisis = emergency!

•   Physical exam: Fatigable weakness (e.g., more pronounced ptosis with sustained upgaze, more weakness with repeated maneuvers), proximal muscle weakness. Monitor for respiratory compromise with MIF/MEP.

•   Diagnosis: Acetylcholine receptor antibody panel, CK (normal), EMG with repetitive stimulation, CT chest to rule out thymoma

•   Treatment: Pyridostigmine, immunosuppression. If concern for myasthenic crisis, perform plasmapheresis or administer IVIG. If a thymoma is present, remove the thymus.

Lambert-Eaton myasthenic syndrome (LEMS)

•   Pathophysiology: Small cell lung cancer cells can produce antibodies against the pre-synaptic Ca2+ channels, which decreases ACh release.

•   Symptoms: Proximal muscle weakness that improves with use

•   Physical exam: Proximal muscle weakness, areflexia

•   Diagnosis: Voltage-gated calcium channel antibodies. EMG with repetitive stimulation. Evaluate for malignancy.

•   Treatment: Remove malignancy, immunosuppression

Botulism

•   Etiology: Rare illness caused by toxins produced by Clostridium botulinum bacteria; can be spread by food (e.g., home-canned foods) or infect a wound (e.g., occurs with IV drug use)

•   Symptoms: Bulbar symptoms (diplopia, dysarthria, dysphagia), blurry vision followed by descending weakness, urinary retention/constipation

•   Physical exam: Ophthalmoplegia with fixed/dilated pupils (vs. normal pupils in myasthenia gravis), facial weakness no sensory involvement

•   Diagnosis: EMG with repetitive stimulation. Stool and serum botulinum toxin testing

•   Treatment: Medical emergency; intubate if needed; administer antitoxin (local Department of Public Health often maintains supply)