A 17-year-old with schizophrenia recently staed on antipsychotics is brought to casualty with neck rigidity. He has
**Core Concept**
The patient's symptoms are likely due to the extrapyramidal side effects (EPS) of antipsychotic medication, specifically drug-induced parkinsonism. This condition is caused by the blockade of dopamine D2 receptors in the nigrostriatal pathway, leading to decreased dopamine release and subsequent muscle rigidity.
**Why the Correct Answer is Right**
The patient's neck rigidity is most likely caused by the blockade of dopamine D2 receptors in the nigrostriatal pathway, which is responsible for motor control. This blockade leads to decreased dopamine release, causing an imbalance in the dopaminergic system and resulting in EPS such as parkinsonism. The nigrostriatal pathway is a critical component of the basal ganglia circuitry, and its dysfunction is a hallmark of drug-induced parkinsonism.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the patient's symptoms are not consistent with a primary neurological disorder such as meningitis, which typically presents with fever, headache, and altered mental status in addition to neck rigidity.
* **Option B:** This option is incorrect because the patient's symptoms are not consistent with a primary psychiatric disorder such as catatonia, which typically presents with immobility, rigidity, and mutism, but without the extrapyramidal symptoms associated with antipsychotic use.
* **Option C:** This option is incorrect because the patient's symptoms are not consistent with a primary endocrine disorder such as hypothyroidism, which typically presents with fatigue, weight gain, and cold intolerance, but without the extrapyramidal symptoms associated with antipsychotic use.
* **Option D:** This option is incorrect because the patient's symptoms are not consistent with a primary infectious disorder such as sepsis, which typically presents with fever, tachycardia, and altered mental status, but without the extrapyramidal symptoms associated with antipsychotic use.
**Clinical Pearl / High-Yield Fact**
It is essential to recognize the extrapyramidal side effects of antipsychotic medication, including drug-induced parkinsonism, as they can be mistaken for primary neurological disorders. A high index of suspicion and a thorough medication history are crucial in diagnosing and managing these conditions.
**Correct Answer: D. Tardive dyskinesia is not the correct option here.**