Spinal cord disorders
Spinal cord disorders are conditions that damage the ascending sensory or descending motor tracts of the spinal cord, producing characteristic patterns of weakness and sensory loss. Classic examples include syringomyelia, ALS, and subacute combined degeneration.
Spinal cord disorders are diseases and injuries that damage the spinal cord's white matter tracts or gray matter, interrupting the signals that travel between brain and body. Because each tract carries a specific function — the dorsal columns carry vibration and proprioception, the spinothalamic tracts carry pain and temperature, and the corticospinal tracts carry motor commands — the pattern of deficits reveals which parts of the cord are damaged.
Several classic syndromes map cleanly onto this anatomy. Syringomyelia, a fluid-filled cavity in the central cord, damages crossing spinothalamic fibers first, producing a "cape-like" loss of pain and temperature sensation across the shoulders and arms. Brown-Séquard syndrome (cord hemisection) causes ipsilateral motor and proprioceptive loss with contralateral pain and temperature loss below the lesion. Anterior spinal artery occlusion spares only the dorsal columns. Tabes dorsalis, from tertiary syphilis, degenerates the dorsal columns and roots.
Other patterns reflect the cause: subacute combined degeneration from vitamin B12 deficiency damages dorsal columns and corticospinal tracts together; amyotrophic lateral sclerosis (ALS) combines upper and lower motor neuron findings with no sensory loss; and poliomyelitis destroys anterior horn cells, causing pure lower motor neuron weakness.
USMLE Step 1 is fond of spinal cord lesion questions: given a deficit pattern, identify the syndrome, the tract involved, or the underlying cause. Learning each tract's function, where it decussates, and the handful of classic syndromes above covers the large majority of these questions.
Key takeaways
- Spinal cord disorders produce deficit patterns determined by which tracts are damaged.
- Dorsal columns carry vibration and proprioception; spinothalamic tracts carry pain and temperature; corticospinal tracts carry motor signals.
- Syringomyelia causes cape-like pain and temperature loss; Brown-Séquard causes ipsilateral motor and contralateral pain/temperature deficits.
- B12 deficiency causes subacute combined degeneration; ALS causes mixed upper and lower motor neuron signs without sensory loss.
- USMLE Step 1 tests these disorders by matching deficit patterns to syndromes, tracts, and causes.