The Primitive Palmomental Reflex in Amyotrophic Lateral Sclerosis

Background and purpose: The palmomental reflex (PMR) is a primitive reflex that might be released due to inhibition in adulthood. It has been associated with several neurodegenerative conditions. The aim of the present study was to evaluate the frequency of PMR in amyotrophic lateral sclerosis (ALS).

Patients and methods: Non-demented ALS patients (n = 179) were recruited. Two groups of disease controls were enrolled: (a) non-demented patients with other neurological disorders (NC; n = 86, mean age 60 ± 14 years); (b) healthy subjects, healthy controls (HC; n = 175, mean age 61 ± 12 years). PMR was elicited by a brisk stroke along the thenar eminence of the right hand with a key or a pen.

Results: The PMR could be elicited in 46% of the ALS patients, compared to 29% of NC and 16% of HC (p < 0.001). A multivariate analysis showed that bulbar-onset and female gender are associated with an increased risk of PMR.

Conclusion: We demonstrate a higher frequency of the PMR in ALS patients compared to NC or HC. Its expression increases with age, being higher in bulbar-onset patients. Given that the reflex circuit is located in the brain stem, its release due to inhibition might be associated to the presence of a cortico-bulbar tract dysfunction in ALS.