We describe a patient with pseudoradial nerve palsy caused by acute ischaemic stroke (‘cortical hand’) to emphasise how preserved synkinetic wrist extension following fist closure can distinguish this from peripheral causes of wrist drop.
- padial nerve palsy
- pseudoradial nerve palsy
- differential diagnosis
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A 55-year-old woman woke with left hand weakness, unable to extend her wrist and fingers, but without numbness, pain or neck symptoms. On examination, she had moderate weakness of the left wrist and finger extensors. When asked to clench her fist firmly, there was preserved synkinetic wrist extension. The remaining muscle strength was normal, as were reflexes and sensation. MR scan of the brain showed a focal cortical region of restricted diffusion in the right precentral gyrus, indicating acute ischaemia (figure 1). We gave intravenous thrombolysis and she subsequently recovered completely.
This patient’s initial history suggested a left radial nerve palsy, but the lack of typical sensory loss and the preserved synkinetic wrist extension following fist closure pointed to an alternative diagnosis. The clinical distinction between peripheral and central causes of wrist drop clearly helps to guide diagnostic investigations, treatment and prognosis. Asking the patient to clench the fist firmly can simply and effectively discriminate a peripheral from a central wrist drop (figure 2). Normal fist closure causes a synkinetic contraction of the long forearm extensor and flexor muscles, keeping the wrist in a neutral position (neither flexed nor extended), and so allowing a strong finger flexion.1 In a peripheral wrist drop from radial nerve palsy, fist closure (with the arm held out and palm facing the floor) causes further wrist drop, as the synkinetic contraction of the long forearm flexor muscles is not counterbalanced by simultaneous activation of the long extensor muscles. Conversely, in a central wrist drop, there is preserved synkinetic contraction of the long extensor muscles of the forearm: the manoeuvre causes a slight elevation of the clenching hand, sometimes with flexion at the elbow.1
Acute ischaemic stroke should be considered in the differential diagnosis of sudden onset of motor deficit in an isolated peripheral nerve pattern, particularly if there is no pain or sensory loss.2 In pseudoradial nerve palsy due to brain lesions, preserved synkinetic wrist extension following fist closure is a useful clue to the right diagnosis.
Acute ischaemic stroke should be considered among the causes of sudden onset of wrist drop, particularly without pain or sensory loss.
In central wrist drop, there is preserved normal synkinetic contraction of the long forearm extensors when clenching the fist.
In peripheral wrist drop from radial nerve palsy, synkinetic contraction of the long forearm flexors is unopposed, and so fist clenching accentuates the wrist drop.
We thank Andrea Orioli for graphic support.
Contributors FB described the sign and wrote the article. GR collected clinical data. Other authors critically revised the article for important intellectual content.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests FB has received speakers' honoraria from Eisai and PeerVoice, payment for consultancy from Eisai, and travel support from Eisai, ITALFARMACO and UCB Pharma.
Patient consent Obtained.
Provenance and peer review Not commissioned; externally peer reviewed by Simon Rinaldi, Oxford, UK.
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