Unilateral Hand Weakness





Careful examination of the anatomical pattern of unilateral hand weakness helps identify the most likely location of the causative lesion. In some cases, clinical weakness is subtle and the pattern of weakness is more easily identified on needle electromyography (EMG) examination of these muscles.



  • A.

    The rapidity of onset and the duration of weakness should be assessed. Primary motor cortex has significant representation of hand movement, and abrupt-onset isolated hand weakness can be seen with cerebral infarction or hemorrhage affecting the contralateral frontal lobe (“hand knob”). There are often, but not always, other associated neurologic symptoms or signs in this scenario. When concurrent neck or radicular pain is present, cervical radiculopathy should be considered.


  • B.

    Ulnar neuropathy occurs most frequently at the elbow as the ulnar nerve travels through the cubital tunnel, but can also occur at the wrist or even in the hand. Ulnar neuropathy must be proximal to the wrist if there is weakness of medial wrist flexion, since the flexor carpi ulnaris muscle is innervated proximal to the wrist. Similarly, an ulnar neuropathy must be proximal to the wrist if there is sensory loss of the dorsal palm, ring finger, and small finger because the dorsal ulnar cutaneous sensory nerve leaves the ulnar nerve prior to the wrist.


  • C.

    A radial neuropathy with arm extension weakness indicates that the lesion must be in the axilla, which is proximal to the innervation of the triceps muscle. 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 dorsal lateral hand and weakness of the wrist and finger extensors but spares elbow extension. The radial nerve terminates into a superficial radial sensory nerve, which conveys sensation on the dorsal lateral hand, and the posterior interosseous nerve, which innervates wrist and finger extensors. A patient with finger extension and wrist extension weakness without dorsal lateral hand numbness likely has a posterior interosseous neuropathy, although a predominantly motor process such as motor neuron disease, brachial neuritis, or multifocal motor neuropathy should also be considered in the appropriate clinical context.


  • D.

    A medial cord plexopathy is a rare cause of hand weakness and can be easily confused with a C8/T1 radiculopathy clinically. Both cause median and ulnar hand weakness as well as numbness of the ring and small finger and medial hand (since the ulnar sensory fibers arise from the medial cord) and medial forearm (due to involvement of the medial antebrachial cutaneous sensory nerve). A medial cord plexopathy should be suspected when there is a combination of median and ulnar hand weakness but finger extension strength is preserved.


  • E.

    On clinical examination, a C8/T1 radiculopathy cannot be distinguished from a lower trunk plexopathy, as both cause a combination of median and ulnar hand weakness, finger extension weakness, and numbness of the medial forearm, hand, and ring and small fingers. In this instance, nerve conduction studies (NCS) and EMG are indicated. NCS should demonstrate normal sensory responses in the setting of radiculopathy. In a lower trunk plexopathy, the ulnar and medial antebrachial sensory responses should be abnormal.


  • F.

    The anterior interosseous nerve is a branch of the median nerve in the forearm that innervates the pronator quadratus, flexor pollicis longus, and flexor digitorum profundus. There is no sensory component to the anterior interosseous nerve. Weakness of these muscles causes difficulty flexing the distal thumb and index finger. When trying to grasp objects between the thumb and index finger, patients compensate for this weakness by adducting these two digits. A patient with distal thumb and index finger flexion weakness likely has an anterior interosseous neuropathy, although a predominantly motor process, such as motor neuron disease, brachial neuritis, or multifocal motor neuropathy, should also be considered in the appropriate clinical context.


  • G.

    Median neuropathy most frequently occurs at the wrist (carpal tunnel syndrome) but can rarely occur in the forearm. The presence of weakness of median-innervated forearm muscles such as the pronator teres or flexor carpi radialis would not be consistent with carpal tunnel syndrome and indicates a proximal median neuropathy.


Algorithm 27.1


Flowchart for the treatment of a patient with unilateral hand weakness. MRI, Magnetic resonance imaging.

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May 3, 2021 | Posted by in NEUROLOGY | Comments Off on Unilateral Hand Weakness

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