Janiszewski's Symptom

Janiszewski's sign (also known as the bulldog reflex) is a clinical sign described by Polish neurologist Janiszewski in 1926.

It is as follows: when tapping on the zygomatic bone from the side of the lesion of the facial nerve, a contraction of the orbicularis oris muscle is observed and the corner of the mouth is pulled in the opposite direction. This occurs due to paresis or paralysis of the facial nerve on the tapping side.

The mechanism of this reflex is that irritation of the zygomatic bone leads to excitation of the trigeminal nerve on this side. With the facial nerve intact, this excitation spreads to the facial muscles and causes them to contract. However, if the facial nerve is damaged (for example, with neuritis), the conduction of the impulse is disrupted, which leads to a lack of muscle contraction on the side of irritation. Instead, the muscles on the healthy side contract due to the preservation of nerve connections, which causes the corner of the mouth to retract.

Thus, the appearance of the Janischevsky symptom indicates damage to the facial nerve. It is most often observed with neuritis of the facial nerve, but can also occur with other diseases accompanied by weakness of the facial muscles on one side of the face. This symptom helps in diagnosing and assessing the extent of damage to the facial nerve.