Thepalmomental reflex (PMR) orMarinescu-Radovici Sign orKinn reflex orMarinescu Reflex is aprimitive reflex consisting of a twitch of the chin muscle elicited by stroking a specific part of the palm. It is present in infancy and disappears as the brain matures during childhood but may reappear due to processes that disrupt the normalcortical inhibitory pathways. Therefore, it is an example of afrontal release sign.
Thethenar eminence is stroked briskly with a thin stick, from proximal (edge of wrist) to distal (base of thumb) using moderate pressure. A positive response is considered if there is a single visible twitch of the ipsilateralmentalis muscle (chin muscle on the same side as the hand tested).[1]
In their seminal 1920 paper,Gheorghe Marinescu and Anghel Radovici hypothesized that both theafferent (receptive) andefferent (motor) arms of thereflex are on the same side (ipsilateral) to the hand stimulated;[2] this hypothesis remains unsubstantiated.[1]
The PMR has been found to be present more frequently in variousneurological conditions, both localized and diffuse. These includecongenital conditions such asDown syndrome, where it is unclear whether the reflex persists throughout life, or disappears and then re-appears in association with the onset ofAlzheimer disease pathology. The reflex is common in the elderly population and should not be taken as indicative of a dementing process.[1]
A study conducted in a neurosurgical in-patient population showed there is no significant association between the side of the reflex and the side of the hemispheric lesion in patients with unilateral (one-sided)reflexes and unilateral (one-sided) lesions.[3]
Primitive reflexes such as the PMR were classically viewed as signs of disorders that affect thefrontal lobes; this traditional view is questionable, as the reflex has been noted, for example, in cases of one-sided temporal lobe pathology.[1][3]