Sir,We report a case of 20-year-old female who approached with two years history of involuntary and irregular dimpling of hypothenar eminence on left side [Figure 1]. She was a college student and had no other difficulties in using left hand. There was no history of shock like pain radiating from neck to hand. Usually there are no triggering factors but occasionally patient recollects that voluntary flexing of left little finger or tapping over muscle or stress may cause spasms on and off. On examination there was no weakness of intrinsic muscles of hand, no sensory loss, and deep tendon reflexes were intact. The nerve conduction showed normal motor and sensory amplitudes in all four limbs. F waves were also normal. As she was referred to us to rule out anterior horn cell disease, electromyography(EMG) was done which showed spontaneous motor unit potentials (MUPs) in left hypothenar muscles, which was normal in amplitude, duration and configuration and other muscles were also normal. Her mother also had similar complaints since childhood and had dimpling in both the hands with left being more prominent than right.
Figure 1
Palmaris brevis spasm
Palmaris brevis spasmPalmaris brevis (PB) is a small quadrilateral shaped muscle. It arises from the transverse carpal ligament and palmar aponeurosis and is inserted into the skin on the ulnar border of the palm of the hand. Hence its action is to increase dimpling of the hypothenar eminence. The superficial branch ulnar nerve supplies PB whereas most of other intrinsic hand muscles are supplied by deep branch of ulnar nerve. Interestingly, the PB muscle is not under voluntary control and its contraction is strictly involuntary.[1]Palmaris brevis spasm syndrome (PBSS) predominantly present with spontaneous, involuntary and irregular contraction or dimpling of PB muscle. It is not associated with paresthesia or sensory loss. It may be unilateral or bilateral. In some of the previous studies they attributed occupation involving frequent use of mouse and keyboard as possible cause.[2] Most cases of PBSS were due to acquired causes like C8 root compression, ulnar nerve injury or followed by decompressive surgery of ulnar nerve but rest of cases were spontaneous without a known etiology.[1] So far no familial cases have been reported in literature. We report the first case of familial PBSS affecting both mother and daughter. The mechanism of PBSS is probably due to ephatic transmission secondary to stretching of superficial branch of ulnar nerve. Satya murthi et al., postulated that it could be a peripheral equivalent of hemifacial spasm.[3] But the mechanism of the spasm restricted to only PB muscle is unclear.There are reports of lignocaineblock of ulnar nerve abolishing spasm. Few reports of phenytoin and carbamazepine also decreased spasm.[1] Recently injection botulinum toxin has been suggested as treatment of choice in patients with disturbing symptoms. We did not treat our patient as she had no disability. In conclusion PBSS is a rare benign condition which should be differentiated from serious disorders like anterior horn cell disease. The exact etiology or mechanism is not known. It usually requires no treatment unless it is disturbing. Here we report the first case of a rare familial PBSS.
Figure 1