Which is the characteristic pattern seen in Brown-Sequard syndrome?

Explanation

## Correct Answer: B. Contralateral loss of pain sensation Brown-Séquard syndrome results from hemisection of the spinal cord, producing a characteristic dissociated sensory loss pattern. The key discriminator is understanding the **anatomical decussation levels** of different sensory tracts. Pain and temperature sensation (spinothalamic tract) decussate **immediately at the spinal cord segment of entry**, within 1–2 levels. Therefore, damage to the right hemicord causes **contralateral (left-sided) loss of pain and temperature sensation** at and below the lesion level. In contrast, proprioception and vibration (dorsal column–medial lemniscus pathway) decussate at the **medulla**, so they are lost **ipsilaterally** (same side as the lesion). Motor loss is also ipsilateral due to pyramidal tract decussation at the medullary pyramids. This creates the pathognomonic pattern: ipsilateral motor loss + ipsilateral proprioceptive loss + **contralateral pain/temperature loss**. In Indian clinical practice (common after spinal cord trauma, tuberculosis of spine, or demyelinating disease), recognizing this dissociated sensory loss is critical for localizing the lesion to the hemicord and distinguishing it from complete transection (which causes bilateral loss) or dorsal column disease (which spares pain sensation). ## Why the other options are wrong **A. Contralateral loss of joint sense and position** — This is wrong because joint sense and position (proprioception) are carried by the **dorsal columns**, which decussate at the medulla, not in the spinal cord. Therefore, proprioceptive loss is **ipsilateral** to the lesion in Brown-Séquard syndrome, not contralateral. This option reverses the correct sensory dissociation pattern and is a classic NBE trap for students who confuse decussation levels. **C. Contralateral motor functions** — Motor loss in Brown-Séquard syndrome is **ipsilateral**, not contralateral, because the corticospinal tract decussates at the medullary pyramids (above the spinal cord lesion). A hemicord lesion therefore damages already-decussated fibers, causing ipsilateral weakness. This option confuses students who incorrectly assume all contralateral deficits occur with spinal lesions. **D. Ipsilateral loss of complete sensory functions** — Complete sensory loss on one side would indicate **complete hemitransection** or a large lesion affecting all sensory tracts. Brown-Séquard syndrome is characterized by **dissociated sensory loss**—pain/temperature is contralateral while proprioception is ipsilateral. This option misses the hallmark dissociation and would be seen only in severe, extensive cord damage, not the classic syndrome. ## High-Yield Facts - **Spinothalamic tract** (pain/temperature) decussates within 1–2 spinal cord segments → contralateral loss in Brown-Séquard syndrome - **Dorsal columns** (proprioception/vibration) decussate at the medulla → ipsilateral loss in Brown-Séquard syndrome - **Corticospinal tract** decussates at medullary pyramids → ipsilateral motor loss in Brown-Séquard syndrome - Brown-Séquard syndrome produces **dissociated sensory loss**: contralateral pain + ipsilateral proprioception + ipsilateral motor loss - Common Indian causes: spinal tuberculosis, traumatic hemicord injury, demyelinating disease, spinal cord compression from disc herniation - The **level of sensory loss** (pain vs. proprioception) helps localize the lesion to the spinal cord segment ## Mnemonics **BROWN-SÉQUARD PATTERN** **C**ontralateral **P**ain (spinothalamic decussates early) + **I**psilateral **P**roprioception (dorsal columns decussate late at medulla) + **I**psilateral **M**otor (pyramids decussate at medulla). Remember: Pain crosses early, motor/proprioception cross late. **DISSOCIATION RULE** Spinal cord lesion → **dissociated loss** (pain separate from proprioception). Brain/brainstem lesion → **crossed loss** (contralateral motor + contralateral sensory). Use this to distinguish hemicord from medullary syndrome. ## NBE Trap NBE pairs Brown-Séquard with "contralateral sensory loss" to lure students into selecting proprioception (option A) instead of pain sensation. The trap exploits confusion about which sensory tract decussates at which level—students who memorize "contralateral = spinal lesion" without understanding decussation anatomy fall for this. ## Clinical Pearl In Indian spinal TB clinics, recognizing dissociated sensory loss (pain loss with preserved proprioception) on one side is the clinical clue to suspect **early hemicord involvement** before complete paraplegia develops—critical for urgent antituberculous therapy and surgical decompression decisions. _Reference: Robbins & Cotran Ch. 28 (Nervous System); Harrison Ch. 369 (Spinal Cord Disorders)_