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The palmomental reflex (PMR) or Marinesco-Radovici Sign or Kinn reflex or Marinesco Reflex is a
primitive reflex Primitive reflexes are reflex actions originating in the central nervous system that are exhibited by normal infants, but not neurologically intact adults, in response to particular stimuli. These reflexes are suppressed by the development of the f ...
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 normal cortical inhibitory pathways. Therefore, it is an example of a
frontal release sign Frontal release signs are primitive reflexes traditionally held to be a sign of disorders that affect the frontal lobes. The appearance of such signs reflects the area of brain dysfunction rather than a specific disorder which may be diffuse, such ...
.


Eliciting and observing response

The
thenar eminence The thenar eminence is the mound formed at the base of the thumb on the palm of the hand by the intrinsic group of muscles of the thumb. The skin overlying this region is the area stimulated when trying to elicit a palmomental reflex. The word ...
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 ipsilateral
mentalis muscle The mentalis muscle is a paired central muscle of the lower lip, situated at the tip of the chin. It originates from the mentum of the mandible, and inserts into the soft tissue of the chin. It is sometimes referred to as the "pouting muscle" due ...
(chin muscle on the same side as the hand tested).


Clinical relevance

Gheorghe Marinescu Gheorghe Marinescu (; 28 February 1863 – 15 May 1938) was a Romanian neurologist, founder of the Romanian School of Neurology. History After attending the Faculty of Medicine of the University of Bucharest, Marinescu received most of his medi ...
and Anghel Radovici in their seminal 1920 paper hypothesized that both the afferent (receptive) and efferent (motor) arms of the
reflex In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus. Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...
are on the same side (ipsilateral) to the hand stimulated; this hypothesis remains unsubstantiated. The PMR has been found to be present more frequently in various
neurological Neurology (from el, νεῦρον (neûron), "string, nerve" and the suffix -logia, "study of") is the branch of medicine dealing with the diagnosis and treatment of all categories of conditions and disease involving the brain, the spinal c ...
conditions, both localized and diffuse. These include
congenital A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can ...
conditions such as
Down syndrome Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with physical growth delays, mild to moderate intellectual d ...
, where it is unclear whether the reflex persists throughout life, or disappears and then re-appears in association with the onset of
Alzheimer disease Alzheimer's disease (AD) is a neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As t ...
pathology. The reflex is common in the elderly population and should not be taken as indicative of a dementing process. 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 In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus. Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...
and unilateral (one-sided) lesions.
Primitive reflexes Primitive reflexes are reflex actions originating in the central nervous system that are exhibited by normal infants, but not neurologically intact adults, in response to particular stimuli. These reflexes are suppressed by the development of the ...
such as the PMR were classically viewed as signs of disorders that affect the
frontal lobe The frontal lobe is the largest of the four major lobes of the brain in mammals, and is located at the front of each cerebral hemisphere (in front of the parietal lobe and the temporal lobe). It is parted from the parietal lobe by a groove be ...
s; this traditional view is questionable, as the reflex has been noted, for example, in cases of one-sided temporal lobe pathology.


References

{{reflist, colwidth=30em Reflexes