## Spinal Cord Injury Syndromes in Ankylosing Spondylitis ### Clinical Context Ankylosing spondylitis (AS) causes progressive ossification of the spinal ligaments and fusion of vertebral bodies, making the spine rigid and brittle ("bamboo spine"). Even minor trauma — including a fall from standing height — can cause catastrophic cervical fracture-dislocations. The key clinical findings here are **bilateral upper limb weakness** with **preserved perianal sensation and voluntary anal contraction** (sacral sparing). ### Spinal Cord Injury Syndromes: Differential Diagnosis | Syndrome | Mechanism | Motor Loss | Sensory Loss | Prognosis | |----------|-----------|-----------|--------------|----------| | **Central Cord** | Central gray matter + adjacent white matter (often hyperextension/compression) | Greater upper limb weakness than lower limb | Variable; "cape-like" suspended loss | Best prognosis among incomplete injuries; lower limbs recover better than upper limbs | | **Anterior Cord** | Anterior 2/3 of cord (ischemia, retropulsion) | Complete motor loss below level | Loss of pain/temperature; preserved proprioception/vibration | Poor motor recovery (<10% regain ambulation) | | **Posterior Cord** | Posterior columns damaged | Preserved motor | Loss of vibration and proprioception | Good motor prognosis | | **Complete** | Entire cord transection | Total motor loss | Total sensory loss including perianal | No recovery | ### Why This Is Central Cord Syndrome **Key Point:** The hallmark of **central cord syndrome** is disproportionately greater weakness in the **upper limbs compared to the lower limbs**, combined with sacral sensory sparing. This patient presents with bilateral upper limb weakness and preserved perianal sensation and voluntary anal contraction — the classic picture of central cord syndrome with sacral sparing. The anatomical basis: in the cervical cord, corticospinal tract fibers are somatotopically arranged with **cervical fibers most medial** (central) and **sacral/lumbar fibers most lateral** (peripheral). A central cord injury preferentially damages the cervical motor fibers while sparing the peripheral sacral fibers, explaining: - **Upper limb > lower limb weakness** (cervical fibers most affected) - **Preserved perianal sensation and anal contraction** (sacral fibers spared peripherally) In AS, the rigid fused spine is vulnerable to hyperextension injuries even with minor trauma, causing buckling of the ligamentum flavum into the central cord — the classic mechanism of central cord syndrome. ### Why Anterior Cord Syndrome Is Incorrect Here Although retropulsion of bone can cause anterior cord syndrome, the **defining feature of anterior cord syndrome** is loss of pain and temperature sensation below the level with preserved proprioception and vibration — the stem does not describe this sensory dissociation. More importantly, the clinical pattern of **bilateral upper limb weakness with sacral sparing** is the textbook presentation of central cord syndrome, not anterior cord syndrome. ### Prognostic Implications **High-Yield:** Central cord syndrome has the **best prognosis** among incomplete spinal cord injuries. Lower limb motor function typically recovers before upper limb function, because the peripheral corticospinal fibers (serving lower limbs) are relatively spared. Bladder dysfunction is common but often improves. Approximately 50–75% of patients regain functional ambulation. **Clinical Pearl:** In elderly patients with cervical spondylosis or AS, hyperextension injuries — even without fracture — can cause central cord syndrome. The presence of sacral sparing (preserved perianal sensation, voluntary anal contraction) is the key finding that confirms an **incomplete** injury and predicts a better prognosis than complete transection. [cite:Harrison 21e Ch 377] [cite:Robbins 10e Ch 28] [cite:Winn HR, Youmans & Winn Neurological Surgery, 7e] 
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