A 52-year-old man from Delhi presents with a 3-month history of progressive weakness in both lower limbs with spasticity. On examination, he has hyperreflexia and bilateral Babinski sign. Vibration and proprioception are intact, but he has loss of pain and temperature sensation below the level of T6 dermatome bilaterally. Gait is stiff and scissor-like. MRI spine shows a central cord lesion at T5–T6 with syrinx formation. Which spinal tract is most likely damaged to explain the dissociated sensory loss?

Explanation

## Clinical Presentation Analysis The patient exhibits a **central cord syndrome** pattern with: - **Motor signs:** Spasticity, hyperreflexia, bilateral Babinski (upper motor neuron lesion) → corticospinal tract involvement - **Sensory dissociation:** Loss of pain and temperature bilaterally below T6, but preserved vibration and proprioception ## Spinal Tract Anatomy | Tract | Decussation Level | Sensation Carried | Lesion Pattern | |-------|-------------------|-------------------|----------------| | **Spinothalamic** | Immediately at spinal cord level (1–2 segments above entry) | Pain, temperature | Contralateral loss below lesion | | **Dorsal column** | Medulla (internal arcuate fibers) | Vibration, proprioception | Ipsilateral loss below lesion | | **Corticospinal** | Medullary pyramids (90%) | Motor control | Contralateral weakness below lesion | ## Why Spinothalamic Tract? **Key Point:** The spinothalamic tract (STT) decussates **within 1–2 spinal segments** of where primary sensory neurons enter the cord. In a **central cord lesion**, crossing fibers of the STT are damaged early and bilaterally, producing **bilateral loss of pain and temperature** while sparing the dorsal columns (which run peripherally and decussate much higher in the medulla). This pattern is called **dissociated sensory loss** or **suspended sensory level** — a hallmark of central cord pathology. **Clinical Pearl:** Central cord syndrome (often from syrinx, trauma, or demyelination) classically spares vibration and proprioception because dorsal column fibers are located laterally and posteriorly, away from the central gray matter where STT fibers cross. **High-Yield:** The STT is the **only major sensory tract that decussates at the spinal cord level itself**. All other sensory pathways decussate in the brainstem or thalamus. This is why central cord lesions produce the characteristic pain/temperature loss with preserved proprioception. **Mnemonic:** **SPINOTHALAMIC = Spinal Immediate Decussation** — remember it crosses right at entry, not higher up.