Tabes dorsalis vs Subacute combined degeneration and Friedreich ataxia
How to tell Tabes dorsalis and Subacute combined degeneration and Friedreich ataxia apart when a board question makes them look alike.
Tabes is neurosyphilis dorsal columns/roots; SCD is B12 posterior plus lateral columns; Friedreich is inherited early ataxia with heart/skeletal clues.
Side by side
Tabes dorsalis is late neurosyphilis with dorsal column and dorsal root involvement causing lightning pains, sensory ataxia, positive Romberg, impaired vibration/proprioception, Argyll Robertson pupils that accommodate but do not react to light, and absent reflexes.
Subacute combined degeneration is B12-related posterior column plus corticospinal tract dysfunction; Friedreich ataxia is inherited early ataxia with cardiomyopathy, pes cavus, scoliosis, and GAA repeat expansion.
Treponema pallidum damages dorsal columns and dorsal roots years after infection.
B12 deficiency impairs myelin in posterior columns and lateral corticospinal tracts; Friedreich causes frataxin-related mitochondrial degeneration of sensory and motor tracts.
Positive syphilis serology with dorsal column signs, lightning pains, and Argyll Robertson pupils that accommodate but do not react to light supports tabes dorsalis.
Low B12/high methylmalonic acid supports SCD; GAA repeat expansion, cardiomyopathy, and early onset support Friedreich ataxia.
The trap
Sensory ataxia overlaps, so syphilis clues, B12 labs, age, and cardiomyopathy separate them.
The repair move
For posterior-column disease, pair the tract finding with infection, vitamin, or inherited-systemic clues.
Try a free question
CoreA patient has lightning leg pains, sensory ataxia, positive Romberg sign, impaired vibration sense, absent reflexes, Argyll Robertson pupils that accommodate but do not react to light, and positive syphilis serology. Which diagnosis is most likely?
Show answer and explanation
Answer: A. Tabes dorsalis. Late neurosyphilis with dorsal column/root findings, lightning pains, and Argyll Robertson pupils supports tabes dorsalis.
Why the other choices are tempting
- B. SCD has B12 deficiency and corticospinal tract signs.
- C. Friedreich ataxia is inherited early ataxia with cardiomyopathy and skeletal findings.
- D. MS causes CNS demyelinating relapses rather than late syphilis dorsal root syndrome.
- E. ALS is motor neuron disease with preserved sensation.
Flashcards
Tap a card to flip it.
What pupil finding supports tabes dorsalis?
Argyll Robertson pupils that accommodate but do not react to light support tabes dorsalis in late neurosyphilis.
What pain clue supports tabes dorsalis?
Lightning pains support tabes dorsalis.
Quick answers
What is the fastest way to tell Tabes dorsalis from Subacute combined degeneration and Friedreich ataxia?
Tabes is neurosyphilis dorsal columns/roots; SCD is B12 posterior plus lateral columns; Friedreich is inherited early ataxia with heart/skeletal clues.
What is the key clue for Tabes dorsalis?
Tabes dorsalis is late neurosyphilis with dorsal column and dorsal root involvement causing lightning pains, sensory ataxia, positive Romberg, impaired vibration/proprioception, Argyll Robertson pupils that accommodate but do not react to light, and absent reflexes.
What is the key clue for Subacute combined degeneration and Friedreich ataxia?
Subacute combined degeneration is B12-related posterior column plus corticospinal tract dysfunction; Friedreich ataxia is inherited early ataxia with cardiomyopathy, pes cavus, scoliosis, and GAA repeat expansion.
What is the common trap with Tabes dorsalis vs Subacute combined degeneration and Friedreich ataxia?
Sensory ataxia overlaps, so syphilis clues, B12 labs, age, and cardiomyopathy separate them.