JendrassikGrof

JendrassikGrof sign is a neurological phenomenon in which a voluntary muscle contraction away from the tested reflex enhances the response of deep tendon reflexes, most commonly the knee-jerk (patellar) reflex. It is used during neurological examination to improve the reliability of reflex testing when reflexes are diminished or difficult to elicit.

Mechanism of action is not fully understood, but it is thought to involve increased excitability of spinal motor neurons through supraspinal pathways and heightened muscle spindle sensitivity during concurrent voluntary contraction. This can reduce competing inhibitory influences and make the reflex more prominent.

Procedure typically involves the patient performing a distraction maneuver while the reflex is being tested. The patient may interlock fingers and pull outward or tense another muscle group, such as the shoulders or jaw, or clench the teeth. The clinician taps the patellar tendon as the maneuver is performed, and an augmented reflex response is observed if present. Variations of the maneuver include different forms of voluntary contraction to achieve a similar effect.

History and nomenclature: the sign bears the names of Ernő Jendrassik and István Grof, Hungarian physicians who described the phenomenon in the late 19th to early 20th centuries. It is sometimes called the Jendrassik maneuver or Jendrassik sign; in some texts the hyphenated Jendrassik-Grof sign is used.

Clinical significance: the sign remains a standard, noninvasive tool in the neurological examination to aid assessment of reflex integrity, particularly when patient factors or body habitus make reflexes harder to observe. It should be interpreted alongside other clinical findings.