[Electromyography of the infrahyoid muscles - part 2: pathological findings]

The infrahyoid muscles (IHM) can easily be used as a neurovascular myofascial flap for reconstructive surgery in the oral cavity and pharynx and especially for functional tongue reconstruction following tumor ablation.

In order to detect neurogenic lesions caused by neck pathologies, in particular lymph node metastasis, we studied ten patients (nine patients suffering from tongue carcinoma and one patient after traumatic tongue ablation) by preoperative electromyography of the IHM. These results were compared to ten healthy controls.

We found no pathological spontaneous activity with the EMG at rest in any patient. During light voluntary innervation, the motor unit potentials (MUP) were normal in controls and in patients with normal ultrasound, CT scans and histologic examination after neck surgery. When pathologic lymph nodes were found in the neck, the number of polyphasic MUP in the ipsilateral IHM 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). Maximal innervation of the IHM was obtained during head bending and jaw opening. We found no difference in the discharge pattern of both groups.

Due to their extent lymph node metastasis can lead to neurogenic lesions of the cervical ansa of the IHM. Neurogenic damages are most clearly present after traumatic lesions of the neck (prior operations, radiotherapy). EMG at maximal voluntary contraction instead revealed no lesions. The clinical impact of these demonstrated neurogenic lesions need to be studied by measuring the muscle strength of the IHM.