Objective: Case report of paediatric Palmaris Brevis Spasm (PBS)

Background: PBS is a rare movement disorder causing intermittent twitching of the palmaris brevis muscle. This muscle is supplied by the ulnar nerve. The cause of this condtion is unknown but previous cases have been reported to be associated with repetitive trauma to the hand. No paediatric case has been reported in the literature. Previous reports suggested the use of oral phenytoin and carbamazepine for intrusive spasms.

Methods: Case report

Results: This is a 16 year old girl presented with sudden onset of intermittent twitching of her left hand. No previous history of repetitive trauma. She denies any sensory symptoms or motor weakness. Her symptoms are more pronounced when she is relaxed. She denies any neck pain. There is no family history of movement disorder. 

On examination she has intermittent twitching of her left palmaris brevis muscle. There is no muscle wasting or twitching of other muscles. Upper limb power examination was entirely normal. Upper limb deep tendon reflexes are also normal and symmetrical. 

MRI imaging of cervical spine and head was normal. Antibodies against VGKC-complex and CASPR2, and KCN1A mutation for EA1 were negative. NCS showed normal ulnar sensory responses. No evidence of focal nerve ulnar nerve entrapment at the elbow or across the wrist.  Needle EMG to the left palmaris brevis showed no evidence of spontaneous activity. There is intermittent firing of motor units which are consistent with the twitching. Normal needle EMG of left adductor digiti minimi. 

The abnormality is confined to the palmaris brevis muscle. She was treated with direct botulinum toxin injection; it abolished palmaris brevis muscle spasm for several months. 

Conclusions: PBS is a rare movement disorder entity. Cause is usually unknown. It is worth to exclude focal nerve entrapment, and cervical pathology. We describe the first idiopathic paediatric case of spontaneous onset of palmaris brevis spasm in a child with no history of trauma or injury.

References: Liguori R, Donadio V, Di Stasi V, Cianchi C, Montagna P. Palmaris brevis spasm: An occupational syndrome. Neurology. 2003;60:1705–7

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MDS Abstracts - https://www.mdsabstracts.org/abstract/palmaris-brevis-spasma-rare-cause-of-paediatric-movement-disorder/