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Science News: Heteronymous H Reflex in Temporal Muscle as a Sign of Hyperexcitability in ALS Patients

Submitted by Elliot Bodofsky, MD
Edited by Clark Pinyan, MD

Heteronymous H Reflex in temporal muscle as a sign of hyperexcitability in ALS patients. Libonati L, Barrone TF, Ceccanti M, et al, Clinical Neurophysiology 130 (2019): 1455-59.

Amyotrophic Lateral Sclerosis (ALS) is a severe neurodegenerative disorder involving both upper and lower motor neurons (UMN and LMN). Diagnosis is mainly clinical, and takes an average of one year after the onset of clinical symptoms. Diagnostic tests are limited. EMG/NCS shows only LMN involvement in affected regions. Better diagnostic tools are needed. Stimulation of the Masseteric nerve can induce an H Reflex in the Masseter and the Temporal muscles. In normal subjects, the Temporal H Reflex is usually only seen with muscle contraction. But it can be seen at rest in ALS with Corticonuclear tract involvement.
This study involved 36 patients with definite or probable ALS by standard criteria, and 52 subjects without evidence of neurologic disease or on medications that might affect the test. There were no significant demographic differences between the groups. Needle stimulation of the Masseteric nerve between and condyle and coronoid process of the mandible was used, with surface pickup over the belly of the Temporalis and reference over the forehead.
The Temporalis H Reflex was found in 32/36 (88.9%) of ALS patients and none of the normal subjects. There were no differences in presence between patients with predominantly UMN versus LMN symptoms. This test is quick and fairly inexpensive. Overall, the presence of a resting Temporalis H Reflex may assist in the diagnosis of ALS in patients with predominantly LMN symptoms.

Comments: ALS is a relatively common, severe, and rapidly progressive disorder. It can be difficult to diagnose in the early phases. The Temporalis H Reflex appears to be a quick, sensitive, and specific test that may help detect it sooner. However, this study included a variety of ALS patients, so it is not clear whether the very high sensitivity would be seen in early cases.

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