Ulnar Tunnel Syndrome
Ulnar tunnel syndrome is an entrapment neuropathy of the ulnar nerve characterized by pain, numbness, and paresthesias of the wrist that radiate into the ulnar aspect of the palm and dorsum of the hand and the little finger and the ulnar half of the ring finger.
These symptoms also may radiate proximal to the nerve entrapment into the forearm. The pain of ulnar tunnel syndrome is often described as aching or burning, with associated “pins and needles” paresthesias.
Similar to carpal tunnel syndrome, ulnar tunnel syndrome occurs more commonly in women than in men. Also similar to carpal tunnel syndrome, the pain of ulnar tunnel syndrome is frequently worse at night and worsened by vigorous flexion and extension of the wrist.
The onset of symptoms usually follows repetitive wrist motions or from direct trauma to the wrist, such as wrist fractures, or direct trauma to the proximal hypothenar eminence, such as may occur when the hand is used to hammer on hubcaps or from handlebar compression during long-distance cycling.
Ulnar tunnel syndrome also is seen in patients with rapid weight gain, rheumatoid arthritis, or Dupuytren disease or during pregnancy. Untreated, progressive motor deficit and ultimately flexion contracture of the affected fingers can result.
Ulnar tunnel syndrome is caused by compression of the ulnar nerve as it passes through Guyon canal at the wrist. The most common causes of compression of the ulnar nerve at this anatomical location include space-occupying lesions, such as ganglion cysts and ulnar artery aneurysms; fractures of the distal ulna and carpals; and repetitive motion injuries that compromise the ulnar nerve as it passes through this closed space.
This entrapment neuropathy manifests most commonly as a pure motor neuropathy without pain, which is due to compression of the deep palmar branch of the ulnar nerve as it passes through Guyon canal. This pure motor neuropathy manifests as painless paralysis of the intrinsic muscles of the hand. Ulnar tunnel syndrome also may manifest as a mixed sensory and motor neuropathy. Clinically, this mixed neuropathy manifests as pain and the previously described motor deficits.
What are the Symptoms of Ulnar Tunnel Syndrome
Physical findings include tenderness over the ulnar nerve at the wrist. A positive Tinel sign over the ulnar nerve as it passes beneath the transverse carpal ligament is usually present. If the sensory branches are involved, decreased sensation occurs into the ulnar aspect of the hand and the little finger and the ulnar half of the ring finger.
Depending on the location of neural compromise, the patient may have weakness of the intrinsic muscles of the hand as evidenced by the inability to spread the fingers, weakness of the hypothenar eminence, or both.
How is Ulnar Tunnel Syndrome diagnosed?
Electromyography helps distinguish cervical radiculopathy, diabetic polyneuropathy, and Pancoast tumor from ulnar tunnel syndrome. Plain radiographs are indicated in all patients who present with ulnar tunnel syndrome to rule out occult bony pathological processes.
Based on the patient’s clinical presentation, additional tests, including complete blood cell count, uric acid level, erythrocyte sedimentation rate, and antinuclear antibody testing, may be indicated.
Magnetic resonance imaging (MRI) and ultrasound imaging of the wrist is indicated to help confirm the diagnosis and whether joint instability or a space-occupying lesion is suspected. The injection technique described here serves as a diagnostic and therapeutic maneuver.
Similar findings to CTS on MRI have been described in the much less common UTS in which entrapment of the ulnar nerve is seen within the ulnar tunnel (Guyon’s canal). Similar to CTS, the role of MRI is not well defined and is probably most useful for the identification of unusual causes such as a mass lesion, anomalous muscle belly, and ulnar artery aneurysm.
Ulnar tunnel syndrome often is misdiagnosed as arthritis of the carpometacarpal joints, cervical radiculopathy, Pancoast tumor, and diabetic neuropathy.
Patients with arthritis of the carpometacarpal joint usually have radiographic evidence and physical findings suggestive of arthritis. Most patients with a cervical radiculopathy have reflex, motor, and sensory changes associated with neck pain, whereas patients with ulnar tunnel syndrome have no reflex changes, and motor and sensory changes are limited to the distal ulnar nerve.
Diabetic polyneuropathy generally manifests as symmetrical sensory deficit involving the entire hand, rather than limited in the distribution of the ulnar nerve. Cervical radiculopathy and ulnar nerve entrapment may coexist as the “double crush” syndrome. Because ulnar tunnel syndrome is commonly seen in patients with diabetes, diabetic polyneuropathy usually occurs in patients with diabetes with ulnar tunnel syndrome.
Pancoast tumor invading the medial cord of the brachial plexus also may mimic an isolated ulnar nerve entrapment and should be ruled out by apical lordotic chest radiographs.
Initial treatment of the pain and functional disability associated with ulnar tunnel syndrome should include a combination of nonsteroidal antiinflammatory drugs (NSAIDs) or cyclooxygenase-2 (COX-2) inhibitors and physical therapy. Local application of heat and cold also may be beneficial. The repetitive movements that incite the syndrome should be avoided.
For patients who do not respond to these treatment modalities, injection of the ulnar nerve at the ulnar tunnel with a local anesthetic and steroid may be a reasonable next step. Ultrasound guidance may improve the accuracy of needle placement and decrease the incidence of needle-related complications.
If the symptoms of ulnar tunnel syndrome persist, surgical exploration and decompression of the ulnar nerve are indicated.
The major complication associated with ulnar tunnel syndrome is due to delayed diagnosis and treatment of the disease. This delay can cause permanent neurological deficits resulting from prolonged untreated entrapment of the ulnar nerve.
Failure of the clinician to recognize an acute inflammatory or infectious arthritis of the wrist may result in permanent damage to the joint and chronic pain and functional disability.
Ulnar tunnel syndrome should be differentiated from cervical radiculopathy involving the C8 spinal root, which sometimes may mimic ulnar nerve compression.
Cervical radiculopathy and ulnar nerve entrapment may coexist in the double crush syndrome. The double crush syndrome is seen most commonly with ulnar nerve entrapment at the wrist or carpal tunnel syndrome. Pancoast tumor invading the medial cord of the brachial plexus also may mimic isolated ulnar nerve entrapment and should be ruled out by apical lordotic chest radiographs.