Syringomyelia is one of those “classic but testable” spinal cord lesions that shows up in vignettes where one sensory modality disappears while others stay intact—and the answer choices are designed to punish superficial pattern recognition. If you learn why the correct choice is correct (and why each distractor is wrong), you’ll start getting these questions right even when the vignette is dressed up.
Tag: Neurology > Peripheral Nerve & Spinal Cord
The Q-Bank Vignette (Classic Presentation)
A 28-year-old woman has progressive difficulty using her hands for the past year. She frequently burns herself while cooking but says her “sense of touch is fine.” Neuro exam shows bilateral loss of pain and temperature over the shoulders and upper extremities in a cape-like distribution. Light touch, vibration, and proprioception are intact. Upper extremity reflexes are decreased.
Question: Where is the lesion and what’s the mechanism?
Correct Answer: Syringomyelia (Central Cavitation of the Spinal Cord)
What’s happening?
A syrinx (fluid-filled cavity) expands in the central spinal cord, most often in the cervical region, and compresses structures in a predictable order.
Why does pain/temperature go first?
Because the first fibers to get hit are the decussating (crossing) second-order neurons of the spinothalamic tract in the anterior white commissure, near the central canal.
- Lost: Pain + temperature (spinothalamic) in a bilateral, segmental pattern
- Spared: Dorsal column modalities (vibration, proprioception, fine touch)
“Cape-like” distribution—why?
The syrinx frequently involves C5–T1 segments, so symptoms map to shoulders/arms.
Common associations (high yield)
- Chiari I malformation (most classic association)
- Cerebellar tonsils herniate through foramen magnum
- Often presents in adolescents/young adults with headaches (worse with Valsalva) + syrinx symptoms
- Can also be due to trauma, tumor, arachnoiditis
Anatomy You Must Visualize (Test-Day Mental Map)
Tract involvement by location
| Structure (spinal cord) | Function | Syringomyelia effect |
|---|---|---|
| Anterior white commissure | Crossing spinothalamic fibers | Early loss of pain/temp (bilateral, “cape-like”) |
| Anterior horn (LMN) | Motor neurons to limbs | Hand weakness, atrophy, fasciculations (LMN signs) |
| Lateral corticospinal tract (UMN) | Motor control to limbs | Later: spasticity, hyperreflexia below lesion |
| Dorsal columns | Vibration/proprioception | Often spared early (lesion is central) |
High-yield phrase
“Dissociated sensory loss” = pain/temp lost with intact vibration/proprioception.
How Q-Banks Trick You: Every Answer Choice Matters
Below are common distractors that appear with this vignette—and the specific clue that rules each one in or out.
Distractor 1: Amyotrophic Lateral Sclerosis (ALS)
Why it’s tempting: Hand weakness and progressive motor symptoms.
Why it’s wrong here:
- ALS is purely motor (no sensory loss).
- Exam would show combined UMN + LMN signs without a sensory level.
Key differentiator:
Syringomyelia causes pain/temp loss; ALS does not.
Distractor 2: Posterior Cord Syndrome (Dorsal Column Lesion)
Examples: Tabes dorsalis, vitamin B12 deficiency (subacute combined degeneration affects dorsal columns + corticospinal)
Why it’s tempting: Spinal cord tract question + “sensory changes.”
Why it’s wrong here:
- Dorsal column lesions impair vibration/proprioception and cause sensory ataxia.
- Syringomyelia spares dorsal columns early.
Key differentiator:
If the patient can’t feel vibration or has a positive Romberg, think dorsal columns, not syrinx.
Distractor 3: Anterior Spinal Artery Infarct
Why it’s tempting: It affects pain/temp (spinothalamic) and motor pathways.
Why it’s wrong here:
- ASA infarct typically causes sudden onset deficits.
- Produces bilateral loss of motor + pain/temp below the lesion, with dorsal columns spared—but it’s not segmental “cape-like.”
- Often includes bowel/bladder dysfunction depending on level.
Key differentiator:
Acute onset and broad deficits below a level → vascular.
Slow, segmental cape distribution → syringomyelia.
Distractor 4: Brown-Séquard Syndrome (Hemisection of the Cord)
Why it’s tempting: Classic spinal cord localization.
Why it’s wrong here: Brown-Séquard gives a very specific split:
- Ipsilateral LMN signs at the level (anterior horn)
- Ipsilateral loss of vibration/proprioception below (dorsal columns)
- Ipsilateral UMN weakness below (corticospinal)
- Contralateral pain/temp loss below (spinothalamic; crosses 1–2 levels above entry)
Syringomyelia is bilateral pain/temp loss at the level(s)—not contralateral loss below.
Key differentiator:
Hemisection → asymmetric findings.
Syrinx → bilateral, suspended pain/temp loss.
Distractor 5: Multiple Sclerosis (MS)
Why it’s tempting: Young adult with neurologic symptoms.
Why it’s wrong here:
- MS lesions are disseminated in time and space: optic neuritis, INO, sensory deficits, weakness, etc.
- Sensory loss patterns in MS aren’t typically segmental bilateral pain/temp with dorsal column sparing.
- MS is CNS demyelination, not a focal central cord cavitation.
Key differentiator:
MS tends to produce multifocal findings and episodic relapses; syringomyelia produces a level-dependent pattern.
Distractor 6: Radiculopathy (e.g., cervical disc herniation)
Why it’s tempting: Upper extremity symptoms.
Why it’s wrong here:
- Radiculopathy follows a dermatomal pattern and often features shooting pain.
- Syringomyelia is bilateral and often affects a “cape-like” distribution, not a single dermatome.
- Radiculopathy wouldn’t selectively knock out pain/temp while sparing fine touch across multiple levels.
Key differentiator:
Dermatome + radiating pain → root.
Cape-like bilateral suspended pain/temp → central cord.
High-Yield USMLE Facts to Lock In
1) The core concept: anterior white commissure
The syrinx hits the crossing spinothalamic fibers → bilateral pain/temp loss.
2) “Suspended sensory loss”
Symptoms can be present at certain levels (e.g., shoulders/arms) while legs are spared early.
3) Motor findings evolve with expansion
- Early: LMN signs at level (hand weakness, atrophy)
- Later: UMN signs below level (spasticity, hyperreflexia)
4) Association with Chiari I
If the vignette includes:
- Headaches worse with coughing/straining
- Neck pain
- Cerebellar signs
…think Chiari I → syringomyelia.
Quick Self-Check: 3 Questions to Ask on Test Day
-
Is pain/temp loss bilateral and segmental (cape-like)?
→ points to syringomyelia. -
Are dorsal column modalities intact?
→ supports “dissociated sensory loss.” -
Is onset progressive rather than acute?
→ supports syrinx over vascular infarct.
Takeaway
Syringomyelia isn’t just “cape-like pain/temp loss.” It’s a central cord lesion that first disrupts the anterior white commissure (spinothalamic crossing fibers), then may expand to involve LMN and later UMN pathways. The distractors are all plausible spinal cord or motor neuron diseases—until you force them to explain the dissociated sensory loss pattern.