Radovici Sign (Palmomental Reflex)
What It Is
The Radovici sign, also known as the palmomental reflex (PMR), is a primitive reflex characterized by involuntary contraction of the mentalis muscle (chin muscle) in response to mechanical or electrical stimulation of the thenar eminence of the palm 1, 2.
How to Elicit the Reflex
Perform a brisk, firm stroke or scratch on the thenar eminence (base of the thumb) using a blunt object or your fingernail, moving from the wrist toward the thumb. Observe the ipsilateral (same side) chin for contraction of the mentalis muscle, which appears as a brief wrinkling or puckering movement 2, 3.
Key Technical Points:
- The stimulus should be applied with moderate pressure—light touch may be insufficient
- The reflex can also be elicited from the hypothenar eminence, though less reliably 3
- The response is typically ipsilateral to the stimulated palm
- In some cases, bilateral chin responses may occur, particularly in pathological states 3
Clinical Significance
A strong, sustained, and easily repeatable palmomental reflex that can be elicited from multiple areas beyond just the palm is more likely to indicate cerebral pathology 2. The mere presence or absence of the reflex has limited diagnostic value because it frequently appears in normal individuals and may be absent in disease states 2.
When PMR Suggests Pathology:
The reflex becomes clinically significant when it demonstrates these characteristics 2, 4:
- Strong and sustained contraction (not just a brief flicker)
- Non-habituating (doesn't diminish with repeated testing)
- Easily and consistently reproducible
- Lateralized or asymmetric (suggests contralateral pyramidal or extrapyramidal lesion)
- Elicitable from areas beyond the thenar eminence
Associated Conditions:
PMR abnormalities may indicate 1, 2, 4:
- Frontal lobe lesions (most common association)
- Pyramidal tract dysfunction
- Extrapyramidal disorders (including Parkinson's disease, where bilateral responses and shorter latencies are characteristic) 3
- Neurodegenerative diseases
- Cerebrovascular disorders
- Traumatic brain injury
- Diffuse cerebral dysfunction
Important Caveats
The palmomental reflex is present in approximately 50% of normal adults, making its mere presence a poor screening tool 2. Focus instead on the quality and characteristics of the response rather than simple presence/absence. A weak, habituating reflex that requires precise localization to elicit is likely within normal limits, while a brisk, sustained, non-habituating response—especially if bilateral or elicitable from multiple sites—warrants further neurological investigation 2, 4.
The reflex represents a primitive brainstem-mediated response that is normally suppressed by higher cortical centers. Its pathological reemergence suggests loss of cortical inhibition 1.