[Omohyoid muscle syndrome in a patient with Parkinson's disease]

A 49-year-old man noticed a resting tremor in his right hand and was diagnosed with Parkinson's disease (PD) at the age of 43. Soon thereafter, he noticed a right neck mass that only appeared when he swallowed and was accompanied by an uncomfortable sensation. At the age of 49, he was admitted to our hospital to adjust his medication for PD and to examine the neck mass. The subcutaneous mass was round, soft, and approximately 3 cm in diameter. The symptoms in his neck showed no progression. Resting tremors and rigidity due to his PD were predominantly observed on his right side, but his postural reflex was intact. Cervical echogram revealed that the mass was the belly of the OM itself. Thus, the patient was diagnosed with omohyoid muscle syndrome (OMS). It can be surmised that some susceptibility of the OM itself and/or structural fragility in the surrounding tissues would be involved in the pathogenesis of OMS. In this case, considering that OMS occurred soon after symptoms of PD appeared, we speculated that muscle tone abnormalities due to PD played a role in the development of OMS.