Unilateral hand numbness is a common complaint with multiple potential causes. Careful examination of the anatomical pattern of the numbness helps identify the most likely location of the causative lesion.
The rapidity of onset and the duration of numbness should be assessed. Primary sensory cortex has significant representation of hand sensation, and abrupt-onset isolated hand numbness can be seen with cerebral infarction or hemorrhage affecting the contralateral parietal lobe. There are usually, but not always, other associated neurologic symptoms or signs in this scenario. When concurrent neck or radicular pain is present, cervical radiculopathy is the most likely diagnosis.
In the setting of abrupt-onset hand numbness with negative brain and cervical spine imaging, acute peripheral nervous system injury should be considered. Examples include compressive nerve injuries or trauma.
Dorsal hand numbness is less common than numbness of the palmar surface. If a patient is unable to precisely localize the pattern of dorsal hand numbness, then radial and ulnar neuropathies and lower cervical radiculopathies (C6/C7/C8) are all possible.
Many patients are unable to localize the distribution of their hand numbness; they may state that their “whole hand” is numb when in fact a mononeuropathy or single radiculopathy accounts for their symptoms. It is useful to ask the patient to compare the degree of numbness present in the medial compared to lateral portions of the hand, as often this leads to recognition of a more localized sensory disturbance. If the pattern of sensory loss remains unclear, one should proceed to test for muscle weakness as outlined here, as this may still help identify the lesion location.
In a patient with isolated ring and small finger numbness, ulnar neuropathy is the most common cause, but a C8 radiculopathy or, even less likely, a brachial plexopathy is possible. Ask about neck pain and radicular symptoms, but in the absence of weakness or hyporeflexia, the clinical examination cannot precisely localize the source of their symptoms. In this instance, nerve conduction studies and needle electromyography (NCS/EMG) are indicated.
A radial neuropathy that spares the triceps is most commonly seen as part of a “Saturday night palsy,” in which the patient experienced prolonged compression of the radial nerve at or near the spinal groove, distal to the innervation of the triceps. This results in numbness of the dorsal forearm and hand and weakness of the wrist and finger extensors but spares elbow extension.
In a patient with numbness of the lateral hand without weakness, carpal tunnel syndrome is the most common cause, although a C6 or C7 lesion is also possible. Ask about neck pain and radicular symptoms, but NCS/EMG is needed to conclusively determine the affected location.
In a patient with lateral hand numbness and biceps or triceps weakness, a C6 or C7 radiculopathy is most likely but a brachial plexopathy is possible. This is more easily distinguished on NCS/EMG. NCS should demonstrate normal sensory responses in the setting of radiculopathy. In an upper trunk or lateral cord injury, the median and lateral antebrachial sensory responses should be abnormal.
In a patient with medial hand numbness and weakness of the first dorsal interosseous, abductor digiti minimi, abductor pollicis brevis, and extensor indicis proprius muscles, a C8 or T1 radiculopathy is most likely but a brachial plexopathy is possible. NCS should demonstrate normal sensory responses in the setting of radiculopathy. In a brachial plexus injury the ulnar and medial antebrachial sensory responses should be abnormal.