Archive for August, 2012

Peripheral nerve disorders comprise a wide variety of pathologies.  Most prevalent are compressive entrapments, with carpal tunnel syndrome and cubital tunnel syndrome being some of the most common.  A peripheral nerve may be compressed at any point from where the nerve roots exit the spinal cord to their insertion into muscles.  However, common points of compression exist.  The key in diagnosing entrapment location is knowing the innervation patterns of each nerve, the common points of entrapment, and classic clinical signs and examination findings.

The median nerve supplies motor innervation to most of the forearm flexors and a few intrinsic hand muscles.  It supplies sensory innervation to the palmar surface of the thumb, index finger, middle finger, and part of the ring finger.  Compression of this nerve most commonly occurs in the wrist underneath the transverse carpal ligament.  The etiology is controversial but probably is caused by a combination of structural, genetic, and repetitive hand use factors.  Certain diseases such as hypothyroidism, acromegaly, amyloid, and diabetes can also lead to compression.  Symptoms of entrapment are mainly numbness, paresthesias, and pain.  Numbness and paresthesias are experienced in the sensory distribution of the nerve.  Generalized palmar numbness is not carpal tunnel syndrome, but may represent compression of the median nerve elsewhere.  Numbness usually occurs during sleep (due to a flexed wrist posture).  Pain may also occur in the nerve’s sensory distribution.  Weakness may be present, but almost always occurs following chronic entrapment.  Sensory changes always precede motor changes and are more sensitive for diagnosis.  Atrophy of the muscles between the thumb and index finger (thenar atrophy) may be present as well.

The ulnar nerve supplies motor innervation to one and a half forearm flexors and most of the intrinsic hand muscles.  It supplies sensory innervation to the palmar surface of part of the ring and entire pinky finger.  Compression of this nerve most commonly occurs in the elbow.  The ulnar nerve passes from the upper arm into the forearm just medial to the olecrenon of the ulna in the postcondylar groove.  It then passes between and under muscles to enter the forearm.  This is called the cubital tunnel.  The etiology of compression is usually trauma or arthritis in the elbow (tardy ulnar palsy).  Symptoms usually insidiously present as paresthesias in part of the ring and pinky fingers.  Weakness of the hand intrinsics may occur at the same time or even as the sole presenting finding.  With chronic compression, classic signs may develop such as Froment’s sign, Wartenberg’s sign, or hand clawing.  Hypothenar atrophy may also be present.

When entrapment is suspected, nerve conduction studies and electromyography are useful in validating the degree of injury and location, but clinical exam findings are the key to diagnosis.  The general distribution of clinical symptoms will identify which nerve (ie. ulnar, median, radial, etc.) is involved.  But the exact location of compression is more difficult to decipher.  Detailed testing of sensory deficits and key motor groups are crucial steps.  As branches exit off each main nerve at different points, isolative testing of individual muscles will determine, for example, if compression of the ulnar nerve is in the cubital tunnel of the elbow or Guyon’s canal in the wrist.  However, more common and classic examination maneuvers may be useful as well.  For both median and ulnar compression, tapping the wrist or elbow (Tinel’s sign) may reproduce the sensory complaints.  This is positive in ~60% of cases.  Using the contralateral extremity as a control helps to validate results.  For median nerve compression, flexing the wrists and opposing them (Phalen’s sign) may also reproduce the symptoms and is positive ~80% of the time.  For ulnar nerve compression, Froment’s sign may be seen by having the patient grasp a piece of paper between the thumb and index finger pads.  Pulling the paper will cause the patient to use the tip of the thumb instead, as the flexor pollicis longus substitutes for the weak adductor pollicis.  Wartenberg’s sign is characterized by an abducted pinky finger caused by weakness of the interosseous muscles.  Patients may complain that their pinky finger gets caught as they place their hands in their pockets.  A claw hand deformity may also be present.

Treatment of both carpal tunnel and cubital tunnel syndromes usually starts with conservative therapy.  Carpal tunnel syndrome commonly resolves with rest, NSAIDs, wrist splinting, and steroid injections.  Cubital tunnel syndrome is treated by avoiding any activities that exacerbate compression (such as repetitive extreme elbow flexion or resting the elbow on hard surfaces), protective elbow sleeves, splinting, and steroid injections.  Patients whose symptoms progress, despite conservative measures, and those who present with weakness, muscle atrophy, or significant denervation on nerve conduction studies should be considered for surgical treatment.

Carpal tunnel syndrome is surgically treated by making a small incision over the wrist and proximal palm and transecting the transverse carpal ligament.  This procedure may be performed using minimal sedation or a nerve block, and patients commonly go home the same day.  Cubital tunnel syndrome is a more involved procedure requiring the patient to undergo general anesthesia.  An incision is made over the medial elbow and the muscles and ligaments over the nerve are either decompressed or the nerve itself is transposed underneath forearm muscles to relieve compression.  Patients are still able to go home the same day.

For an evaluation or possible surgical treatment of peripheral nerve entrapment, please call The Neurosurgery Center of Colorado at 303-481-0035 to make an appointment with Dr. Adam P. Smith, MD.

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