A 52-year-old man from Delhi presents to the neurology clinic with a 3-month history of progressive weakness in both lower limbs and loss of pain and temperature sensation in the lower trunk and bilateral legs, while vibration and proprioception remain intact. He reports a history of spinal tuberculosis treated 2 years ago. On examination, he has bilateral lower limb weakness (grade 3/5), brisk reflexes, and bilateral Babinski sign. Sensory examination shows a clear sensory level at T10 with loss of pain and temperature below this level, but preserved vibration and proprioception. MRI shows cord compression from an old healed lesion with syrinx formation. Which spinal cord tract is most likely damaged, causing this dissociated sensory loss pattern?

Explanation

## Clinical Presentation Analysis The patient demonstrates a classic pattern of **dissociated sensory loss** — loss of pain and temperature sensation with preserved vibration and proprioception. This selective sensory deficit is the hallmark of spinothalamic tract involvement. ### Anatomical Basis of Dissociated Sensory Loss **Key Point:** The spinothalamic tract (STT) carries pain and temperature information via crossed fibers in the anterior and lateral columns, while the dorsal columns (fasciculus gracilis and cuneatus) carry vibration and proprioception via uncrossed fibers in the posterior columns. ### Spinal Cord Tract Comparison | Tract | Sensory Modality | Crossing Pattern | Location | Lesion Effect | |-------|------------------|------------------|----------|---------------| | **Spinothalamic** | Pain, Temperature | Crosses 1–2 segments above entry | Anterolateral cord | Loss of pain/temp below lesion | | **Dorsal Columns** | Vibration, Proprioception | Does NOT cross in spinal cord | Posterior cord | Loss of vibration/proprioception below lesion | | **Corticospinal** | Motor control | Crosses at medullary pyramids | Lateral cord | Weakness, hyperreflexia, Babinski | | **Dorsal Spinocerebellar** | Proprioception (unconscious) | Uncrossed | Lateral cord | Ataxia, not sensory loss | ### Why This Pattern Occurs 1. **Spinothalamic tract fibers** decussate (cross) within 1–2 spinal segments of their entry point via the anterior white commissure. 2. **Dorsal column fibers** ascend ipsilaterally without crossing until they reach the medulla, so they are spared in mid-thoracic cord lesions. 3. A lesion at T10 compressing the anterolateral cord selectively damages the crossed STT fibers while preserving the posterior dorsal columns. **High-Yield:** This dissociated sensory loss (pain/temp loss + preserved vibration/proprioception) is **pathognomonic for spinothalamic tract involvement** and distinguishes it from dorsal column disease, which causes the opposite pattern. ### Clinical Correlation The patient also has: - **Bilateral lower limb weakness and hyperreflexia** → corticospinal tract involvement (expected with cord compression) - **Sensory level at T10** → level of maximal cord compression - **Syrinx formation** → post-traumatic syrinx from old TB lesion, causing progressive myelopathy **Clinical Pearl:** Syrinx expansion can progressively damage multiple tracts over time; the dissociated sensory loss indicates the syrinx is affecting the anterolateral spinothalamic fibers preferentially. [cite:Standring Anatomy 41e Ch 4]