Ulnar Neuropathy

Etiology

The second most common upper extremity entrapment neuropathy is ulnar neuropathy at the elbow (UNE). At the elbow, the ulnar nerve lacks protective cover in the ulnar groove. This causes its susceptibility to external compression. Repetitive elbow flexion and extension, arthritic changes, and valgus deformities at the elbow increase its vulnerability to injury. In some individuals, the ulnar nerve may be subluxed out of the retroepicondylar groove medially over the medial epicondyle during elbow flexion. In a study investigating patients with UNE, the pressures recorded between the ulnar nerve and overlying arcade increased up to above 200 mm Hg in elbow flexion or during isometric contraction of the flexor carpi ulnaris muscle. In contrast, the pressure was less than 19 at elbow extension.[2]

Repetitive movement that exerts pressure on the ulnar wrist and hypothenar eminence predisposes the ulnar nerve to develop neuropathy. Wrist fractures and compressive mass lesions may also cause ulnar neuropathy at the wrist (UNW).

Epidemiology

There are limited studies of incidence and prevalence rates for ulnar neuropathy. In a study in the general population in Italy, incidence was 20.9%, with males affected more than females.[3] In a population-based survey in Egypt, crude prevalence rates showed that ulnar neuropathy at the elbow was the second most common type of entrapment.[4]

Pathophysiology

Neurapraxia of the ulnar nerve is often seen with mild injury. However, moderate-to-severe injuries of the nerve will present as axonotmesis, or in severe cases, neurotmesis.

History and Physical

Symptoms of ulnar neuropathy at the elbow usually start slowly unless it is associated with trauma. The patient may have numbness and paresthesia,  radiating distally to the ulnar aspect of the hand, the fifth digit and the ulnar aspect of the fourth digit. It is usually associated with elbow flexion, particularly at night. Unless it is associated with an acute injury to the elbow, pain is not a dominant feature; however, some patients may complain of pain due to overuse of the forearm flexors such as the FCU.

 Sensory symptoms involving the fifth digit and medial half of the fourth digit may indicate an ulnar neuropathy at the wrist. However, similar findings can be seen in ulnar neuropathy at the elbow. It is suggested that the fibers destined for the FCU, PUC, and DUC lie in individual fascicles at the elbow in a deep dorsolateral position, rendering them less susceptible to damage.[5]This renders them less susceptible to injury in UNE, and may cause difficulty in distinguishing UNE from ulnar neuropathy at the wrist. However, if there is an involvement of the entire ring finger or in contrast, total sparing, the diagnosis of cervical radiculopathy or brachial plexopathy should be taken into account.

When the disease gets worse, the symptom may progress to constant numbness and paresthesia and weakness of the innervated muscles. Weakness may start from clumsiness and loss of hand dexterity. This may then progress to a decrease in handgrip and pinch strength (Froment sign). In more severe cases, there may be atrophy of the hand intrinsic muscles and clawing of the fourth and the fifth digits, classically known as claw hand.[6]

Ulnar neuropathy at the wrist and hand can range from pure sensory to pure motor deficits. The most common type of ulnar neuropathies at the wrist is compression of the deep palmar branch. Ulnar neuropathies of the wrist and hand are divided into 3 types. Type I is a lesion of the ulnar nerve just proximal to or within the Guyon canal involving deep and the superficial branches; this causes mixed motor and sensory deficits and subsequent weakness of all the ulnar hand muscles. Type II is a lesion involving the deep branch which causes a pure motor deficit with a varied pattern of weakness based on the compression site. Type III lesion is limited to the superficial branch, causing purely sensory deficits to the palmar aspect of the medial half of the fourth digit and the fifth digit. The sensory loss in type I and type III lesions spares the dorsal aspect of the hand and fingers and the hypothenar eminence due to the more proximal innervations from the DUC and the PUC, respectively.[7]

Evaluation

Diagnosis traditionally relies on clinical history, physical examination, and electrodiagnostic studies. It has been suggested that combination of electromyography (EMG) and nerve conduction velocity (NCV) tests can improve diagnostic accuracy by mapping out the location of pathological compression of the ulnar nerve, which would provide a relatively early diagnosis in patients who have symptoms suggestive of ulnar nerve lesions.

Ultrasound (US) has also been suggested as a screening and follow-up imaging modality in patients with ulnar neuropathy at the elbow, as US can detect the morphologic changes and the extent of the ulnar nerve lesion at the elbow. A recent meta-analysis showed that in healthy participants, the ulnar nerve cross-sectional area at various locations at the elbow rarely exceeds 10 mm, and this can be considered a cutoff point for diagnosing ulnar nerve entrapment at the elbow region.[8] Another study suggested that by measuring ulnar nerve cross-sectional area with MRI or US at 1-cm proximal to the medial epicondyle, patients with and without UNE could be discriminated by using a cutoff threshold of 11.0 mm.[9] It is also suggested that the ulnar nerve-swelling ratio can be a complementary tool for diagnosing ulnar neuropathy at the elbow, and other potential sonologic indicators include presence of intra-neural vascularity, increased flattening ratio, and enlarged intra-neural hypoechoic fraction, although further research is needed.[10]

Treatment / Management

There are 2 main conservative treatments:  reducing the frequency of external compression on the nerve and flexion of the elbow joint. This is expected to decrease the stress placed on the ulnar nerve. The use of elbow splints, elbow pads or sleeves, and physical therapy have been suggested. For patients with mild to moderate symptoms, conservative treatment can be administered. It was shown that in patients with mild symptoms, conservative treatments are proven to be beneficial in about 90% of the patients; however, only 38% of the patients with moderate symptoms respond well a non-operative method.[11]

Injection procedures have also been proposed for the treatment of ulnar neuropathy at the elbow. However, studies with ultrasound-guided corticosteroid injections at the elbow have shown controversial results.[12][13](A1)

Surgical treatment becomes a consideration for patients with persistent symptoms, with accompanying sensory changes and muscle atrophy. Several surgical methods have been described, for example, decompression, anterior transposition techniques, and medial epicondylectomy. A systematic review showed that simple decompression and decompression with transposition are equally effective in idiopathic UNE. However, the decompression surgery with transposition is associated with more wound infections than simple decompression.[14](A1)

Differential Diagnosis

• Alcohol-related neuropathy

• Amyotrophic lateral sclerosis

• Brachial plexus abnormalities

• Cervical disc disease

• Epicondylitis

• Pancoast tumour

• Thoracic outlet syndrome

• Traumatic peripheral nerve lesions