21- Compression Neuropathies Flashcards
When do compression neuropathies occur?
Compression neuropathy occurs when pressure on a peripheral nerve produces sensory, motor, or autonomic changes/dysfunction in that nerve
What nerve is affected in carpal tunnel?
median nerve at the wrist.
What nerve is affected by cubital tunnel?
ulnar nerve at the elbow.
What is the epineurium?
outer covering that cushions the entire nerve against external pressure and contains concentric layers of dense collagenous CT
What is the perineurium?
middle layer surround the fascicle, each containing a group of axons; it’s the analogue of the BBB b/c it controls the intraneural environment (it limits diffusion, blocks entry of bacteria, etc., and maintains a slightly positive intrafascicular pressure)
What is the endoneurium?
a collagen shell the surrounds each axon
How does the axon get blood?
segmental nutrient veseels in the epineurium feed into perineurial plexi, which penetrate the endoneurium to feed the axon.
What does compression of a nerve do to the blood supply?
- impaired venous return
- intraneural edema
- altered ionic milieu
What does compression of a nerve do to the signal conduction?
Diminished axoplasmic transportation and decreased efficiency of the Na2+ pump promote membrane instability and impede signal conduction.
What occurs at 30-40mmHg compresison of a nerve?
neurophysiologic changes
What occurs at >60mmHg compression of a nerve?
complete intraneural ischemia –> total sensory block
What is epineural fibrosis?
happens with prolonged compression
• exacerbates intraneural edema
• decreases signal transmission
• leads to permanent nerve dysfunction
What would happen if a nerve is teathered to the surroinding tissue?
If a nerve is tethered, its normal physiologic motion that occurs with joint motion is limited; this places the nerve at risk for traction injuries in response to repetitive joint motion
What are the Sx of carpal tunnel?
pain, numbness, and weakness in the median n. distribution of the hand
What amatomical structures make up the carpal canal where the median n. passes through?
- transverse carpal ligament on the palmar surface
2. carpal bones on the dorsal surface.
What muscles does the median n. supply?
1,2 LOAF: Lumbricals 1 & 2, opponens pollicis, abductor pollicis brevis, flexor pollicis brevis
What is the most common of the compression neuropathies?
Carpal tunnel syndrome (2% of population)
What are the risk factors for carpal tunnel syndrome (CTS)?
older age, occupation, health status, rheumatoid arthritis, endocrine disorders (e.g. diabetes mellitus and hypothyroidism), trauma, hormonal changes (e.g. w/ pregnancy, menopause), presence of masses (e.g. lipomas and ganglions).
What are the early Sx of CTS
vague wrist pain w/ numbness/tingling in the thumb, index, long fingers, and radial half of the ring finger.
What are the later Sx of CTS?
pain at night in the distal forearm/palm and hand/fingers.
What are the Long-standing CTS Sx?
sense of grip weakness (denervation of thenar mm—abductor pollicis brevis and opponens pollicis); difficulty w/ fine motor activities (decreased proprioception); waking in the night with pain if the wrist assumes a flexed position during sleep
Which activites exasterbates the Sx of CTS?
activities that place the wrist in a prolonged flexed or extended position (typing, bicycling)
What are the signs of CTS?
• Atrophy and loss of sweating in the fingers innervated by the median n.
• Decreased 2-point discrimination (i.e. decreased ability to discern correctly btwn 2 pins on the fingertips placed a few mm apart)
o can be quantified by identifying the min. distance btwn pins recognized by the pt. as 2 distinct points of contact
• Weakness (although weakness can reflex poor effort or inhibition caused by PAIN)
What 2 proximal things must you check for on physical exam for CTS?
- ) proximal sources of compression (cervical spine)
2. ) masses in carpal canal
