Flashcards in Week 6 Overview of Neuromuscular Disorders Deck (17)
Define the components of the motor unit
1. Anterior horn cell
2. Peripheral nerve (axonal part)
3. Peripheral nerve (myelin part)
4. Neuromuscular junction (presynaptic & postsynaptic)
Know which components of the motor unit are affected in neurogenic, junctional and myopathic disorders
-Neurogenic: anterior horn cell, peripheral nerve-axonal and myelin part
-Neuromuscular junction disorders: Neuromuscular junction
-Myopathic disorders: muscle
What do you look at to differentiate between neurogenic, junctional, and myopathic disorders? And to localize the problem.
1. muscle weakness distribution
2. presence of sensory function abnormality
3. presence or absence of reflexes
4. presence or absence of fatigability/diural variation
5. mode of spread of weakness
6. presence or absence of cramps or fasiculations
List the diagnostic laboratory tests and what type of disorders they are abnormal in.
1. Serum CPK: elevated in myopathic disorders
2. Nerve conduction studies: abnormal in neurogenic diseases
3. Repetitive nerve stimulation studies: abnormal in neuromuscular junction disorders
4. electromyographic evaluation
5. muscle or nerve biopsy: to diagnose muscle or neurogenic disorders
What is the etiology and age of onset of Amyotrophic lateral sclerosis (ALS)?
This is a anterior horn cell disorder
-etiology is unknown, sporadic.
-age of onset: mid/late years of life
What are the clinical features of ALS?
-purely motor with asymmetric, predominantly distal, proximal, or bulbar muscle weakness
-sparing of extra ocular and sphincter muscles
-cramps and fasciculations common
-progression of disease: muscle atrophy and wasting, respiratory and swallowing impairment
What are the typical findings of diagnostic tests in ALS?
-CPK normal to slightly increased
-nerve conduction normal
-EMG and muscle biopsy show denervation and reinnervation features
What is the etiology and of Guillain Barre Syndrome (GBS)?
This is a peripheral nerve disorder, demyelinating neuropathy
-etiology: immune mediated
What are the clinical features of GBS?
-starts in lower extremities and moves up to involve upper extremities and some CNs
-mild sensory complaints
-predominant motor weakness and disability
-respiratory muscle involvement common, rapid progression
-autonomic symptoms secondary to autonomic nerve involvement
What are the typical findings of diagnostic tests in GBS?
-abnormal nerve conduction studies
-cellular infiltrates indicative of inflammatory disorder in nerve biopsy
What is the etiology of myasthenia Gravis?
Autoimmune. Antibodies against nicotinic acetylcholine receptors.
Age of onset: various
What are the clinical features of myasthenia gravis?
-symptoms begin in extra ocular and cranial nerve innervated muscles followed by proximal muscle weakness
-fatigability worsened by activity
-diurnal variations characteristic
-ptosis, double vision, dysphagia, nasal voice, weakness of jaw closure, neck extensors with proximal muscle weakness, respiratory muscle involvement
What are the typical findings of diagnostic tests in myasthenia gravis?
Abnormal repetitive stimulation tests
elevated nicotinic Ach receptor antibody titer
abnormal thymic tissue
What is the etiology of Lambert-Eaton Myasthenia Syndrome (LEMS)? What is age of onset?
-Autoimmune, paraneoplastic, secondary to small cell lung cancer
-age of onset: mid-late years
What are the clinical features of LEMS?
-patients present with fatigue, proximal muscle weakness, and autonomic dysfunction (cholinergic hypo function)
What is the etiology of inflammatory myopathy?
Autoimmune. Common associated with various collagen vascular diseases. Can be manifestation of remote cancer.