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Diff Dx: Ulnar Nerve Dysfunction

- Systemic conditions: (may mimic ulnar entrapment syndrome at elbow)
    - Syringomyelia
    - Amyotrophic Lateral Sclerosis
    - Entrapment of the ulnar nerve distally at the wrist (Guyon's canal)
    - Snapping Elbow Syndrome:
         - syndrome which has yet to be fully described, in which patients note recurrent snapping along the medial aspect of the elbow;
         - may either be due to anomalous triceps muscle insertion or due to recurrent subluxation of ulnar nerve (which occurs from a 
                deficient cubital tunnel);

- Anatomic Lesions;
    - C-spine: (see clinical exam)
         - compression of cervical roots can cause radiating paresthesias in the hand;
         - C-8 (C7-T1 disk) & T1 root can best be distinguished from ulnar nerve by pattern of muscle weakness;
                - the correct diagnosis is made by noting the function of muscles innervated by the C-8 and T1 portions of the median nerve; 
                       (ie, the function of index and long FDP, FPL, and thenar muscles);
         - Spinal cord tumor
         - Extramedulary spinal lesions
                - neurofibroma
                - meningioma
                - lesions of the brachial plexus or medial cord
    - Thoracic Outlet:
         - rarely, brachial plexus is involved by metastatic tumor or by thoracic outlet syndrome.
         - consider Pancoast Tumor;
    - Elbow:
         - medial epicondylitis is an associated complication;
         - cubital tunnel syndrome
              - potential causes of ulnar entrapment, in approx order of frequency, are as follows:
              - cubital tunnel syndrome, external compression, previous frx & scarring, recurrent subluxation of nerve, & entrapment;
         - recurrent ulnar nerve subluxation:
              - may occur in upto 16-20% of population;
              - as the elbow flexes, the ulnar nerve may sublux anteriorly over the epicondyle;
              - references:
                      - Recurrent ulnar-nerve dislocation at the elbow. 
                      - Ulnar nerve strains at the elbow.
         - snapping ulnar nerve sydrome:
              - snapping of the medial head of the triceps over the medial epicondyle may occur by itself or may occur along with ulnar nerve 
              - triceps snapping may occur as the elbow is flexed or as it is extended  from a flexed position;
              - failure to recognize this syndrome intra-operatively, can lead to clinical failure of ulnar nerve transposition;
    - Wrist:
          - ulnar nerve can be compressed at wrist rather than elbow by repeated trauma to palm (often occupational) or by ganglion or tumor;
          - numbness over dorsum of the hand may be seen in Cubital Tunnel Syndrome in contrast to compression within Guyon's canal 
                (where dorsal sensory numbness would not be expected;
          - in addition, ulnar nerve compression at the wrist would not be expected to cause weakness of the FCU, nor weakness of the little 
                and ring FDP muscles

Snapping of the medial head of the triceps and recurrent dislocation of the ulnar nerve.  Anatomical and dynamic factors.