Syringomyelia is a disorder characterized by a fluid-filled, gliosis-lined cavity (syrinx) within the spinal cord. The condition most commonly affects the cervical to upper thoracic region (C2–T9) and leads to selective damage of neural pathways, particularly the anterior white commissure.
Pathophysiology
- The syrinx expands within the central canal of the spinal cord, compressing the decussating fibers of the lateral spinothalamic tract, which are responsible for pain and temperature sensation.
- As the lesion enlarges, it can extend into the anterior horns, causing lower motor neuron (LMN) weakness in the upper limbs.
Clinical Features
| Feature | Explanation |
|---|---|
| Loss of Pain & Temperature | “Cape-like” distribution over the shoulders and upper extremities due to spinothalamic tract involvement. |
| Preserved Touch & Vibration | The dorsal column (posterior column) is spared. |
| Weakness & Atrophy | LMN signs (flaccid paralysis, areflexia, atrophy) in the hands and arms due to anterior horn damage. |
| Progression | May spread inferiorly and affect multiple dermatomes. |
| Association | Most commonly associated with Chiari I malformation; less often with tumors, trauma, or infections. |
Key Points to Remember
- Location: Cervical spinal cord (C2–T9).
- Tract Affected: Crossing fibers of the spinothalamic tract.
- Sensory Loss Pattern: Bilateral “cape-like” loss of pain and temperature.
- Motor Deficit: LMN weakness in the upper limbs.
- Associated Malformation: Chiari I malformation (herniation of cerebellar tonsils).
Learning Objective
After completing this lesson, the medical student should be able to:
Describe the pathophysiology, clinical features, and neuroanatomical correlations of syringomyelia and identify its distinguishing sensory and motor patterns on the USMLE Step 1.
