Objective: To report retrospective review of seven cases of Hemi masticatory spasm (HMS), supported by electrophysiological and clinical findings.

Background: Hemi masticatory spasm (HMS) is a rare movement disorder affecting muscles of mastication due to dysfunction of motor branch of trigeminal nerve and is characterized by painful spasm of masticatory muscles.

Method: We enrolled a total of 7 patients with HMS (4 males and 3 females) over a period of 4 years (2013-2017) from our institute, a tertiary care referral center in northern part of India.

Results: All patients presented with unilateral painful spasms involving either masseter or temporalis muscles or both, triggered by activities like chewing, talking, clenching of teeth or voluntary tapping of the involved muscles. All patients reported increasing severity and frequency of spasms over time and continuous rippling movements of the jaw during each episode. There was associated Lichen Sclerosus et Atrophicus (LSA) with segmental morphea (involving left side of face & neck, back of trunk, left upper & lower limb) in one patient and localised scleroderma of face in 2 patients. Associated muscle hypertrophy (masseter) was seen in 3 cases (4,5 & 7) and FHA was seen in other cases (1-3, 6). Surface electromyography (EMG) showed spontaneous irregular bursts of high frequency motor unit potentials arising from involved muscles during spasm and disappearance of discharges at rest, ruling out possible functional etiology. Masseter inhibitory reflex (done in 2 patients, case 1, & 6) showed loss of inhibition in form of absent silent period during spasms. All 7 patients initially received phenytoin (dose 250-300mg/day) without any sustainable effect. However both pain and spasms showed excellent response to local Onabotulinumtoxin-A injection in all patients. All of them reported at least 70-80% improvement of pain and spasms (Global subjective assessment) at last follow up.

Conclusion: In this paper we highlight the delay in diagnosis of HMS due to rarity, long course of illness, association with hemiatrophy, “Lichen Sclerosus et Atrophicus” (LSA) and scleroderma / morphea. Considering the favorable outcome to botulinum toxins surgical treatment can be avoided or delayed in majority except secondary cases.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/hemi-masticatory-spasm-hms-series-of-7-cases/