Neuromuscular Diseases Flashcards
Lambert-Eaton myasthenic syndrome (LEMS) vs. Myasthenia gravis (cause, sensitivity to depolarizing and nondepolarizing muscle relaxants, treatment)
- LEMS is a paraneoplastic syndrome where antibodies directed against PRESYNAPTIC CALCIUM CHANNELS markedly reduce the quantal release of Ach at the motor-end plate. It is treated with GUANIDINE HYDROCHLORIDE and 3.4-DIAMINOPYRADINE (DAP), which increase the release of Ach from the presynaptic nerve terminal and leads to significant clinical improvement. LEMS patients are very SENSITIVE TO BOTH DEPOLARIZING AND NONDEPOLARIZING neuromuscular blocking drugs.
- Myasthenia gravis is an AUTOIMMUNE destruction or inactivation of POSTSYNAPTIC Ach receptors at the neuromuscular junction. Patients are RESISTANT TO DEPOLARIZING NMBs but SENSITIVE TO NONDEPOLARIZING NMBs. ANTI CHOLINESTERASE DRUGS are the most commonly used agents for treatment.
What are the definitive signs and symptoms of Lambert-Eaton myasthenia syndrome vs. Myasthenia Gravis
LEMS is characterized by proximal muscle weakness that typically beings in the upper extremities, but may spread to upper limb, bulbar, and respiratory muscles. Male impotence, dry mouth, and autonomic dysfunction are also characteristic. Muscle weakness IMPROVES WITH REPEATED EFFORT and is improved less dramatically with anticholinesterase drugs.
MG is characterized by muscle weakness of the ocular muscles (most commonly affected). Severe disease is associated with proximal muscle weakeness (neck and shoulders) and involvement of respiratory muscles. Muscle strength IMPROVES WITH REST but deteriorates rapidly with exertion.
Describe the common characteristics of myotonic dystrophy
An autosomal dominant disease that presents in the 2nd to 3rd decade of life
It is characterized by:
- Cardiac problems (conduction problems of all types, diastolic dysfunction, and failure)
- Endocrine problems (gonadal dystrophy, adrenal dysfunction, DM, thyroid dysfunction)
- Cataracts and muscle degeneration
How do patients with myotonic dystrophy respond to depolarizing and non-depolarizing muscle relaxants? Reversal drugs?
Succinylcholine can cause hyperkalemic arrest as well as provoke myotony (tetany of the muscles)
Non-depolarizers have prolonged effect
Reversal agents can provoke myotony (as can the twitch monitor)
What are some treatments of myotonic dystrophy?
Membrane-stabilizing medications: phenytoin, quinine-sulfate, and procainamide
What is the most common and severe form of muscular dystrophy?
Duchenne’s muscular dystrophy, an X-linked recessive disorder producing abnormal dystrophin in affected individuals
What are the common physiological problems (cardiac and pulmonary) associated with Duchenne’s muscular dystrophy (DMD)?
Cardiac: dilated or hypertrophic cardiomyopathy, mitral regurgitation (due to papillary muscle dysfunction) is more common than aortic regurgitation, circulatory depression
Pulmonary: Restrictive ventilatory defect (due to combo of kyphoscoliosis and muscle wasting) where all lung volumes are decreased. Pulmonary HTN is seen with disease progression
What drugs may induce generalized myotonia is patients with myotonic dystrophy?
Propofol (due to its inhibition of mitochondrial function placing patients with mitochondrial defects at increased risk for respiratory and cardiac depression, arrhythmias, metabolic disturbances, severe neurological deficits, and propofol infusion syndrome)
Succinylcholine
Neostigmine
Does central core disease have an association with malignant hypothermia (MH)?
CCD is associated with an increased risk of MH
In fact, it has the highest susceptibility to MH of the neuromuscular disorders.
What test is used to diagnose Myasthenia Gravis?
Tensilon test (should see improvement of symptoms)
What kind of pain is typically associated with neurogenic inflammation?
Nociceptive (NOT neuropathic) pain
What electrolyte abnormality has been implicated as a potential cause of neurogenic inflammation?
Magnesium deficiency
Describe the Oxford Standard Muscle Grading System
Muscle strength is graded 0-5 as follows:
- Flicker of movement
- Through full range actively with gravity counterbalanced (eliminated)
- Through full range actively against gravity
- Through full range actively against some resistance
- Through full range actively against strong resistance
What is central sensitization?
It is mediated by different chemical modulators than peripheral sensitization.
Agonism of the NMDA receptors results in the production of glutamate and aspartate which have neurochemical effects and also stimulate the NMDA receptors themselves
Bradykinin, prostaglandin, and substance P play a role
What are treatment options for patients with Guillain-Barre syndrome?
- IV immunoglobulin is effective at preventing progression
- Plasmpharesis reduces the progression if initiated within a week of the onset of the symptoms
- Mechanical support may become necessary if respiratory compromise continues due to weakness or the respiratory muscles.
[Corticosteroids have NOT been proven to be beneficial]
