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
How can you test for CTS using the Tinel’s test?
percussing the median nerve at the wrist can reproduce symptoms of CTS
How can you test for CTS using the median n. compression test?
continued manual compression of the median n. at the entrance to the carpal canal will reproduce Sx
How can you test for CTS using the Phalen’s test?
if the pt. sustains symmetric wrist flexion, Sx of CTS are reproduced
When does weakness of the thenar muscles occur during CTS?
in the advanced stage of the disease
Why must you take an X-ray of the cervicals for CTS pt’s?
helps rule out herniated disk or osteophytic compression of the neural foramina
How does the motor nerve conduction velocity test work?
are performed by electrical stimulation of a peripheral nerve and recording from a muscle supplied by this nerve. The time it takes for the electrical impulse to travel from the stimulation to the recording site = the latency. The size of the response = the amplitude
How does the sensory nerve conduction velocity test work?
are performed by electrical stimulation of a peripheral nerve and recording from a purely sensory portion of the nerve, such as on a finger.
What is pronator syndrome and why is it a differential Dx to CTS?
compression of the median n. at the elbow
• Distinguished from CTS based on involvement of mm. supplied by the median nerve PROXIMAL to the wrist (e.g. involvement of flexor digitorum superficials to ALL fingers)
What is cervical radiculopathy (C6 or C7) and why is it a differential Dx to CTS?
may produce symptoms that overlap w/ CTS
• Seen in pts. w/ cervical disk disease or arthritis
What is cervical instability and why is it a differential Dx to CTS?
may produce a radiculopathy similar to CTS
• Seen in pts. w/ rheumatoid arthritis or trauma
What nerve passes through the Guyon’s canal?
Ulnar n
What structures make up the Guyon’s canal?
floor is made of transverse carpal lig and the palmar carpal ligament makes up the roof
What are the Sx when Guyon’s canal is compressed?
numbness in the little finger and ulnar half of the ring finger and limited motor dysfunction in the intrinsic muscles of the hand.
How can you Dx Guyon’s canal compressions?
percussion over Guyon’s canal usually elicits Sx; confirm with nerve conduction velocity studies.
Why is cubital tunnel syndrome more common than Guyon’s canal syndrome?
Compression of the ulnar n. in the cubital fossa (“cubital tunnel syndrome”) is more common than compression in Guyon’s canal b/c the nerve is more superficial there. May be caused by pt. resting their elbow on hard surfaces during daily activities
What are the Sx of cubital tunnel syndrome?
numbness along the pinky and ulnar half of the ring finger, grip weakness (especially when using tools), dull ache along medial forearm
How can you Dx cubital tunnel syndrome?
percussion along the course of the ulnar n. posterior to the medial epicondyle can reproduce Sx in the fingers; weakness and atrophy may be present in the intrinsic muscle of the hand.
Where is the thoracic outlet?
The thoracic outlet is the space between the clavicle, the 1st rib, and the middle and anterior scalene mm.
What causes thoracic outlet syndrome?
TOS is caused by compression of the vascular or neural components of the brachial plexus in the thoracic outlet where they travel between the anterior and middle scalenes. It typically affects the ULNAR side of the hand
What are the Sx of TOS?
pain, tingling, and numbness along the ulnar half of the hand and forearm
What is the Tx for early-onset nontraumatic CTS?
nonsurgical; night splints that maintain the wrist in a neutral position (decreasing pressure on the median n.); cortisone injections into the carpal canal (may decrease edema in the nerve or tendon sheaths).
What is the Tx for CTS caused by radial fracture OR going on for >1 year?
surgical decompression of the carpal tunnel (very high success in reducing Sx and halting progression).
