Electromyography of the infrahyoid muscles: pathological and normal findings

In recent years, the infrahyoid muscles (IHM) have been used by plastic reconstructive surgeons as a neurovascular muscle flap in the neck and mouth region.

A preoperative electromyographic examination (EMG) of the IHM was performed in 10 patients, of whom 9 suffered from tongue cancer, in order to detect neurogenic lesions caused by possible metastases or lymph nodes. The results were compared to those of 10 healthy controls.

The EMG at rest showed no pathological spontaneous activity in any patient. During light voluntary innervation, the motor unit potentials (MUPs) were normal in controls and in patients with normal sonographic images, computertomographic scans, and histologic findings after surgery in the neck region. When metastatic lymph nodes were found on one side of the neck, the number of polyphasic MUPs in the IHM of that side was increased in some cases (n = 6), and normal in others (n = 5). Traumatic or radiogenic lesions clearly resulted in pathological EMG findings (n = 6). A maximal innervation of the IHM was achieved during head bending and jaw opening, there was no activation of the IHM with tongue movements and vice versa.

If the presence of lymph node pathology was demonstrated using imaging techniques, a resulting lesion of the ansa cervicalis can functionally be demonstrated by EMG. In patients without lymph node metastases and without concurrent other lesions in the cervical region, EMG of the IHM seems to give no further clinical information. A clear postoperative functional differentiation of the transplanted IHM and the indigenous tongue muscles is possible.