A site for medical students - Practical,Theory,Osce Notes

Palmomental reflex –A complete guide

The palmomental reflex (PMR) is a primitive reflex.
Method of elicitation
Scratching or stroking with a blunt point over the thenar area ofpatients  hand 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 chin muscle on the same side as the hand tested. There is also involuntary contraction orbicularis oris muscles .

There are two different neural pathways that may account for the wide range of latencies.
  • The common afferent pathway consists of the cutaneous and muscular receptors of the thenar eminence and the median nerve. 
  • The common efferent pathway involves the motor nuclei of the facial nerve.
  • Longer latencies may involve the thalamus and motor cortex 
  • Shorter latencies may result from brainstem integration of the reflex
Significance of palmomental reflex
Palmomental reflex is present in infancy and disappears as the brain matures during childhood but it may reappear due to processes which disrupt the normal cortical inhibitory pathways.However, the reflex is often present in normal people and may be absent in disease states.
This reflex  is present in pyramidal lesion, UMN facialpalsy, frontal lobe lesion, The reflex is not of value in identifying the site of cerebral pathology(no localising value).
Why it is called as frontal release sign?
The frontal cortex inhibits subcortical motor networks, theoretically, the presence of a frontal lesion alters those inhibitory pathways and the primitive sign is ‘released’
Specific medical conditions associated with palmomental reflex
The reflex is commoner in patients with such neurological diseases as
  • Stroke
  • Multiple sclerosis
  • Motor neurone disease
  • Cerebral tumours.
  • Parkinson’s disease
  • Dementia.
  • Severe head injuries.
  • Down’s syndrome
  • AIDS
  • Vibroacoustic disease