A 48-year-old man with no significant past medical history presents to the emergency department (ED) with a 3- to 4-month history of slowly progressive difficulty with active, but not passive, extension of the ring and little fingers of his right hand. He denies any tingling, numbness, or skin changes in his hands or his forearms. There is no neck pain, and a thorough neurologic review of symptoms, including motor weakness, decrease in proprioception, and 2-point discrimination, is negative.
On physical examination, the patient appears well with normal vital signs. His temperature is 98.6°F (37°C); pulse, 86 bpm; respiratory rate, 18 breaths/min; and blood pressure, 135/85 mm Hg. The patient’s oxygen saturation is 98% while breathing ambient air. The appearance of the patient’s hands is shown in Image 1. The palmar surfaces are noted to be normal, without any skin changes (including rashes or discrete lesions). He has no pain or tenderness in the neck, with a full range of motion. Passive range of motion of the wrist and fingers is normal, with no evidence of increased resistance to movement. Active flexion of the fingers is normal, but all extension of the ring and little fingers of the right hand is absent. The left hand has a normal range of motion, including extension and flexion, of all fingers.
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The examining physician (please note, this was not the author) was also able to guess the patient’s occupation.
Which anatomic structure is affected, and where is it most vulnerable?
HINT
The condition is a classic but less common compression neuropathy.
Author:
Daniel M. Lindberg, MD, Instructor of Medicine – Emergency Medicine, Harvard Medical School. Attending Physician, Department of Emergency Medicine, Brigham & Women’s Hospital, Boston, MA.
eMedicine Editor:
Rick G. Kulkarni, MD, FACEP, Assistant Professor, Yale School of Medicine, Section of Emergency Medicine, Department of Surgery, Attending Physician, Medical Director, Department of Emergency Services, Yale-New Haven Hospital, CT
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ANSWER
Chronic compression ulnar neuropathy: The patient’s hand maintains the classic “clawhand” position for this condition. Chronic compressive ulnar neuropathy is uncommon and has no gender preference. The clinical presentation depends mostly on the location of the compression, the most common sites being either at the cubital tunnel, located at the elbow, or at the Guyon canal (also referred to as the ulnar tunnel), located just distal to the wrist. Similar to the more commonly known condition carpal tunnel syndrome, chronic compressive ulnar neuropathy can be associated either with isolated sensory or motor findings or with a combination of both motor and sensory findings. In this case, the absence of symptoms in the forearm suggested that the point of compression was not likely to be in the cubital tunnel, but, rather, was likely to be in the ulnar tunnel just distal to the wrist, as the ulnar nerve wraps around the hamulus of the hamate. This led the treating physician to infer that the patient worked with a device that intermittently exerted compressive, blunt traumatic forces at that anatomic position; the physician correctly guessed that the patient was a jackhammer operator. A safety feature of the jackhammer is a right-sided trigger on the handle that must be squeezed during operation; this serves to keep the palm in the same position on the handle.
Anatomically, the ulnar nerve lies within the Guyon canal at the wrist. The Guyon canal is the triangular canal at the base of the ulnar side of the palm; it is bordered laterally by the hook of the hamate and the transverse carpal ligament and by the medial wall formed by the pisiform. The ulnar nerve traverses the canal and enters the hand to supply the hypothenar muscles, which include the opponens digiti quinti and the abductor digiti quinti, in addition to the ulnar lumbrical muscles, the interossei of the hand, and the deep branch of the flexor pollicis brevis muscle. The ulnar nerve also supplies sensation to the ulnar aspect of the ring finger and the little finger, in addition to the dorsal ulnar half of the hand and fingers through the dorsal cutaneous branch. As a result, chronic ulnar neuropathy with a component of motor weakness will show atrophy in the innervated muscles and is often seen as wasting of the interosseous muscles, especially the first interosseous muscle. Sensory findings may include numbness, tingling, paresthesias, and pain in an ulnar distribution of the palm and the innervated digits. There may also be cold intolerance in the ring and little fingers and a positive Tinel or Phalen sign. Normal sensation may be noted in the distribution of the dorsal sensory cutaneous branch of the ulnar nerve, which branches off before the ulnar nerve enters the Guyon canal. Ulnar neuropathy can result from compression related to trauma, neoplasm, and abnormal anatomy, or it can be caused by inflammation, as in rheumatoid arthritis, pregnancy, hypothyroidism, or microcirculatory disease. The initial diagnosis is clinical. Two-point discrimination is helpful in diagnosing nerve compression with sensory symptoms. Compression at the affected anatomic location (ie, at the cubital tunnel or the ulnar tunnel) may reproduce symptoms.
A plain radiograph can demonstrate any associated fractures or other bone abnormalities resulting in ulnar nerve compression. Computed tomography (CT) or magnetic resonance imaging (MRI) may be useful for identifying whether a cyst or other growth is causing pressure on the ulnar nerve. Confirmation of the diagnosis and confirmation of the site of compression can be made by electromyography (EMG) or nerve-conduction studies. Although rest, nonsteroidal anti-inflammatory drugs (NSAIDs), and splinting may provide some relief, surgical release is often necessary. The differential diagnosis for a patient with finger-extension difficulties includes dermatologic or tendinous pathologies, such as Dupuytren contracture. Clinically, differentiation is straightforward, even in the absence of the sensory findings of ulnar neuropathy, as Dupuytren contracture is associated with characteristic palmar fibromatosis leading to resistance with passive extension of the affected fingers.
The patient in this case was placed in a Velcro wrist splint and discharged with NSAIDs. A follow-up appointment was arranged with the Hand Surgery department. He was instructed to avoid using jackhammers until appropriate therapy could be carried out. A subsequent EMG confirmed the presence and location of the lesion, and the patient was scheduled for surgical ulnar tunnel release as a definitive treatment for his condition.
References:
1. Latinovic R, Gulliford MC, Hughes RAC. Incidence of common compressive neuropathies in primary care. J Neurol Neurosurg Psychiatry 2006 Feb; 77(2): 263-5 [MEDLINE: 16421136]
2. Wilhelmi BJ, Naffziger R, Neumeister M. Hand, Nerve Compression Syndromes: Upper Extremity. www.emedicine.com [serial online]. Last updated: June 28, 2006. Available at: http://www.emedicine.com/plastic/topic300.htm. Date accessed: September 4, 2007.
3. Stern M, Steinmann SP. Ulnar Nerve Entrapment. www.emedicine.com [serial online]. Last updated: January 8, 2004. Available at: http://www.emedicine.com/orthoped/topic574.htm. Date accessed: September 4, 2007.
