Nerve and Muscle Flashcards
Two tests for Myasthenia gravis:
Tensilon test: edrophonium, a readily reversible ACh esterase inhibitor, or the ice pack test, that can temporarily reverse ptosis.
Myasthenia gravis shows what on EMG?
Decremental response to repetitive stimulation.
What type of antibodies are found in MG?
Anti-ACh receptor, in about 80-90% of patients.
What is MG?
A neuromuscular junction disorder where antibodies block and distort the acetylcholine receptor.
Treatment for myasthenic crisis:
IVIG, plasmapharesis immediately to reduce antibody load in blood, however proactive intubation in an emergency.
What is Lambert-Eaton myasthenic syndrome?
a paraneoplastic disorder. It is characterized by slowly progressive weakness that, in contrast to myasthenia gravis, usually spares eye muscles, and there is a brief improvement in strength with exercise. This is seen on EMG as an incremental response to repetitive stimulation. The mechanism is by the production of antibodies against presynaptic calcium channels.
The tumor most likely to cause Lambert-Eaton myasthenic syndrome is:
Lungs (often small-cell).
Treatment for MG:
Maintenance with pyridostigmine (Mestinon), a reversible cholinesterase inhibitor, steroids (azathioprine) are also standard of care.
What is myasthenic crisis?
Patients will have respiratory insufficiency that is out of proportion to the rest of their muscle weakness or increased generalized weakness of their bulbar muscles necessitating intubation. This is a medical emergency. Patients must be admitted to the ICU and have their respiratory muscle strength monitored with serial FVC measurements.
LP results in GBS:
WBC normal, RBC normal, protein high: this pattern is referred to as albuminocytologic dissociation.
Which infectious agent commonly precedes GBS?
Campylobacter jejuni
Treatment for GBS:
IVIG (easier and less SE), plasmapharesis
Decreased conduction velocity and conduction block indicate a _____.
demyelinating process
What is GBS?
An autoimmune disorder, often following a GI illness, where patients developing ascending weakness with minimal sensory symptoms.
Symptoms develop over hours to days and patients may also have significant back pain due to inflammation of nerve roots.
Loss of reflexes is a key to clinical diagnosis.
Where to look for ulnar nerve symptoms or “claw hand.”
The course of the ulnar nerve around the posterior aspect of the medial epicondyle makes it susceptible to traumatic injury when patients strike the medial epicondyle of the humerus posteriorly, or inferiorly with the elbow flexed, compressing the nerve against the bone.
Drop wrist and numbness on the back of the hand is due to injury of which nerve?
Radial nerve
Injury of femoral nerve presents how?
Weakness of knee extension and hip flexion.
What is lateral femoral cutaneous nerve syndrome?
Meralgia paresthetica: compression of the nerve as it exits the inguinal ligament, presents with sensory symptoms on the lateral thigh and can be treated with weight loss and wearing looser clothes.
Which nerve, when injured, leads to foot drop?
The common peroneal nerve divides into the deep and superficial branches. The deep branch is responsible for foot drop. There is also numbness of the lateral calf and foot.
The tibial nerve is responsible for what?
Foot plantar flexion
The sciatic nerve does what in the leg?
hamstring muscles/knee flexion
C5 and C6 nerve roots mediate which reflexes?
Biceps and brachioradialis
C6 and C7 (mostly C7) mediate which reflex?
Triceps reflex
L3 and L4 (mostly L4) mediates which relfex?
Knee jerk
S1 nerve root mediates which reflex?
Ankle jerk
Periumbilical area is innervated by which dermatome?
T10
Nipple area is innervated by which dermatome?
T4
What causes descending paralysis?
Botulism
What is pseudohypertophy of muscle and when is it seen?
Infiltration with fatty tissue and the muscles are actually breaking down. Duchenne Muscular Dystrophy.
Which gene is mutated in DMD?
dystrophin
What is the mechanism of inheritance of DMD?
X-linked recessive
CK levels in DMD:
Could be 100x normal
DMD treatment:
avoid exercise (injures muscles), weekly steroid treatments, death occurs in the mid 20s.
What is Becker’s MD?
Similar to DMD but milder, patients can often walk into early adulthood.
Ragged red muscle fibers are seen in what?
Mitochondrial myopathies. Abnormal accumulations of mitochondria. Serum or CSF lactate and pyruvate are often increased as well.
What is inclusion body myositis?
> 50 years old, distal muscles of hands/feet, asymmetrical, CK is normal or moderately elevated, thought of as neurodegenerative disease of muscle without effective treatment.
What is polymyositis?
> 18 years old, subacute inflammatory myopathy that is progressive in a “lim-girdle” distribution, often cardiac involvement, CK up to 50x normal, treatment with steroids.
What is dermatomyositis?
Adults and children, heliotrope rash, scaly (mechanic’s) hands, Anti-Jo-1 antibodies, higher likelihood of temporal arteritis, measure ESR, treat with prednisone.
What is hyperkalemic periodic paralysis?
An autosomal dominant disease of sodium channels. Serum and urinary K are high during attacks. Presents before age 10 with acute onset proximal muscle weakness provoked by cold, resting after exercises, potassium rich foods. Treat with acetazolamide.
What is hypokalemic periodic paralysis?
An autosomal dominant disease of calcium channels, early childhood presentation with soreness in back/thighs/limbs, episodes last several hours but start/end abruptly. Provoked by resting after exercise and carb consumption, treat with oral K supplementation.
What is paramyotonia congenita?
Caused by mutation in Na channel, severe stiffness caused by cold exposure, rest, or low K.
What is myotonia congenita?
Caused by a mutation in the chloride channel, presents with muscle stiffness that worsens with rest, improved with exercise.
