Evaluation of upper extremity mononeuropathy

Vasculitis

Rarely presents with upper limb mononeuropathy. Although this is not a common presentation, it should be considered, particularly when there are other symptoms or signs suggestive of vasculitis, such as fever, malaise, weight loss, and/or a vasculitic skin rash. Typically, in vasculitis the onset of mononeuropathy is sudden and associated with severe neuropathic pain. Because vasculitis may progress rapidly, causing serious neurologic and systemic complications, it requires prompt recognition, diagnosis, and management. However, in the absence of a predisposing underlying disease such as systemic lupus erythematosus, vasculitis is often not recognized until the patient has developed a second mononeuropathy (mononeuritis multiplex). See Mononeuritis multiplex.

Rarely, vasculitis can be isolated to the peripheral nervous system, in which case no systemic symptoms and no serologic inflammatory markers occur. Although this diagnosis is obviously challenging, it is exceedingly rare and needs to be considered only in cases with multiple mononeuropathies without other explanations.

Malignancy

Malignant tumors do not generally cause distal mononeuropathies in the upper extremity, but they can invade the brachial plexus resulting in a clinical presentation similar to a distal mononeuropathy. They should be particularly considered in at-risk patients presenting with symptoms suggestive of ulnar neuropathy. As it is typically the lower trunk of the brachial plexus that is involved first, these patients often present with numbness in the fourth and fifth digits and weakness of the hand. The additional presence of any of the following clinical features helps to differentiate this from the more common ulnar neuropathy:

• Severe pain radiating from the neck or shoulder

• Marked atrophy of the thenar eminence and weakness of thumb abduction without median sensory involvement

• Horner syndrome (ipsilateral pupil miosis and ptosis).

Central nervous system lesions

Occasionally lesions in the central nervous system can mimic mononeuropathies. This includes multiple sclerosis, which can present with sensory symptoms mimicking a nerve distribution. Stroke can also occasionally mimic a mononeuropathy with isolated sensory or motor findings in what appears to be a nerve distribution. A careful history and neurologic exam can usually differentiate. These central nervous system lesions rarely present as an upper extremity focal neuropathy.