Posterior cord syndrome can feel like a “weird sensory-only spinal cord lesion” until you anchor it to what the dorsal (posterior) columns actually do: vibration, proprioception, and fine (discriminative) touch. If you can remember those three quickly, you can answer most Step-style questions in under 10 seconds.
The Acronym Trick: P.O.S.T.
Use P.O.S.T. to lock in Posterior cord Syndrome:
- P = Position sense loss (proprioception)
- O = Oscillation loss (vibration)
- S = Sensory ataxia (Romberg positive)
- T = Touch (fine/discriminative) impaired
One-liner
Posterior cord syndrome = loss of dorsal column modalities below the lesion → “can’t feel position/vibration,” causing sensory ataxia with a positive Romberg, while motor and pain/temperature are relatively spared.
Quick Visual/Mnemonic Device (mental picture)
Picture the spinal cord like a backpack:
- The posterior (back) pocket holds “precision sensory gear”:
- vibration
- proprioception
- fine touch
- If that back pocket gets ripped, you drop your precision gear → you stomp-walk and need vision to balance.
Clinically: “I’m fine looking at my feet… but I fall when I close my eyes.”
What You Lose vs What You Keep (High Yield Table)
| Tract / Modality | Posterior (Dorsal) Columns | Spinothalamic | Corticospinal |
|---|---|---|---|
| Vibration | Lost | Intact | Intact |
| Proprioception | Lost | Intact | Intact |
| Fine touch (discriminative) | Lost | Variable | Intact |
| Pain & temperature | Intact (usually) | Spared | Intact |
| Motor strength | Spared | Spared | Spared (unless other tracts involved) |
| Key bedside test | Romberg + | Pinprick/temp | Strength/reflexes |
How It Presents on Exams (Classic Clues)
Look for these buzzwords:
- “Positive Romberg” (falls with eyes closed)
- Sensory ataxia (wide-based, stomping gait)
- Loss of vibration sense (tuning fork on toes/ankles)
- Impaired joint position sense (can’t tell toe up vs down)
- Paresthesias can happen, but the pattern matters
Two quick differentiators
- Cerebellar ataxia: unsteady even with eyes open (Romberg not the main issue)
- Posterior cord syndrome: balance is much worse with eyes closed (vision compensates)
High-Yield Etiologies to Associate with Dorsal Column Damage
Posterior columns are especially vulnerable in a few testable conditions:
Vitamin B12 deficiency (Subacute Combined Degeneration)
- Hits dorsal columns + lateral corticospinal tracts (so not purely posterior cord syndrome)
- Clues: macrocytic anemia, paresthesias, loss of vibration/proprioception, +/- UMN signs
- Common association: pernicious anemia, malabsorption, vegan diet
Neurosyphilis (Tabes dorsalis)
- Dorsal columns + dorsal roots → lightning pains, sensory ataxia
- Clues: Argyll Robertson pupils (accommodate but don’t react), areflexia
Posterior spinal artery infarct
- More rare than anterior spinal artery infarct
- Produces dorsal column deficits (vibration/position) below lesion
Multiple sclerosis
- Can cause patchy dorsal column involvement (varied presentations)
Ultra-High-Yield Bedside Pearl
Romberg tests proprioception (dorsal columns).
- Positive Romberg = patient is stable with eyes open but sways/falls when eyes close → sensory (posterior column) problem.
Mini Rapid-Fire Self-Check (USMLE-style)
Patient has loss of vibration sense in both feet and a positive Romberg; pain and temperature are normal. Where is the lesion?
→ Posterior (dorsal) columns (posterior cord syndrome)