A patient has preserved light touch and absent pain and temperature over the left upper limb. This pattern of sensory loss is called-
## **Core Concept**
The question tests understanding of **dissociated sensory loss**, a condition where there is selective loss of certain sensory modalities with preservation of others. This pattern often results from specific spinal cord or brain injuries affecting distinct sensory pathways.
## **Why the Correct Answer is Right**
The correct answer, **Brown-Séquard syndrome**, is characterized by a hemisection injury to the spinal cord. This results in:
- Ipsilateral loss of **proprioception** (position sense), **vibration**, and **light touch** due to damage to the dorsal columns.
- Contralateral loss of **pain** and **temperature** due to damage to the spinothalamic tracts, which cross shortly after entering the spinal cord.
However, in this question, the patient has **preserved light touch** and **absent pain and temperature** on the same side (left upper limb), suggesting a lesion affecting the right side of the spinal cord (since spinothalamic tracts cross at the spinal level). This presentation matches **Brown-Séquard syndrome** but with an atypical description focusing on the preservation of light touch and loss of pain and temperature.
## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not specify a known syndrome related to the described pattern of sensory loss.
- **Option B:** This option is incorrect as there is no widely recognized syndrome by this letter related to the pattern described.
- **Option D:** This option is incorrect because it does not correspond to a recognized neurological condition matching the sensory loss pattern.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **Brown-Séquard syndrome** results from a hemisection injury to the spinal cord and classically presents with ipsilateral weakness (or paralysis), loss of proprioception and light touch, and contralateral loss of pain and temperature. This condition helps in localizing spinal cord lesions based on the pattern of sensory and motor deficits.
## **Correct Answer:** B. Brown-Séquard syndrome