Painful lockjaw is seen in case of following EXCEPT?
## **Core Concept**
Painful lockjaw, also known as trismus, can result from various conditions affecting the jaw, muscles of mastication, or the nervous system. The question aims to test knowledge of conditions associated with trismus.
## **Why the Correct Answer is Right**
Trismus or lockjaw is commonly associated with tetanus infection, which causes severe muscle spasms. Tetanus toxin affects neurotransmitter release, leading to muscle rigidity and spasms, including the masseter muscles, resulting in lockjaw. This condition is characterized by painful muscle contractions.
## **Why Each Wrong Option is Incorrect**
- **Option A:** Tetanus is a classic cause of painful lockjaw due to muscle spasms.
- **Option B:** Rabies can cause hydrophobia and spasms of the muscles involved in swallowing and, less commonly, can lead to trismus.
- **Option C:** Strychnine poisoning leads to muscle convulsions and spasms due to blocking inhibitory neurotransmission, which can include the muscles of the jaw.
## **Clinical Pearl / High-Yield Fact**
A key clinical point is that tetanus infection often presents with trismus (lockjaw) as an early symptom, alongside risus sardonicus (a spasmodic, involuntary grin). Early recognition can lead to timely intervention.
## **Correct Answer:** D.