Opisthotonus is seen in poisoning with –
**Core Concept**
Opisthotonus is an extreme form of opisthotic posture characterized by an arching of the back and a hyperextension of the neck, resulting in a 'bowing' of the spine. This condition is often associated with severe neurological disorders, including tetanus infection.
**Why the Correct Answer is Right**
Opisthotonus is a classic sign of tetanus infection, caused by the bacterium *Clostridium tetani*. The toxin produced by this bacterium, tetanospasmin, interferes with the release of neurotransmitters that inhibit muscle contraction, leading to sustained muscle spasms and the characteristic opisthotonic posture. This results from the unopposed action of excitatory neurotransmitters, such as glycine and GABA, which normally regulate muscle tone.
**Why Each Wrong Option is Incorrect**
* **Option A:** While strychnine poisoning can cause muscle convulsions, it typically presents with a more generalized and violent muscle spasms, rather than the characteristic opisthotonic posture seen in tetanus.
* **Option B:** Mercury poisoning can cause a range of neurological symptoms, including tremors and muscle weakness, but is not typically associated with opisthotonus.
* **Option C:** Lead poisoning can cause a variety of systemic symptoms, including neurological effects, but is not classically associated with opisthotonus.
**Clinical Pearl / High-Yield Fact**
Tetanus infection is characterized by a 'lockjaw' (trismus) due to spasms of the masseter muscle, which can be a key distinguishing feature from other causes of muscle spasms.
**Correct Answer: C. Lead poisoning can cause a variety of systemic symptoms, including neurological effects, but is not classically associated with opisthotonus.