Subacute Combined Degeneration: How to Diagnose?

  OK, if the MRI's & EP's are negative, and my MS sypmtoms are not MS, but from the Vitamin B12 deficiency, then is the diagnosis SCD?  What is the difference between neurological symptoms from B12 deficiency and SCD?  How do they make that diagnosis?  How long does it take for the neurological symptoms to go away once B12 supplements are started?  If you have had the symptoms for years and years, what are the chances they will actually go away?  Does it make any difference if the supplements are sub-lingual or injected?  Are there any specific tests, etc., to determine the SCD diagnosis?  Any info is appreciated!! Thanks!

[CCF Neuro MD MJD]

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B12 deficiency can cause a number of issues - Anemia, Memory changes and Behavioral problems, and Optic Nerve problems (the nerve from the eye to the brain transmitting visual impulses.  Subacute Combined Degeneration is among the neurologic complications of B12 deficiency and is named so because of the involvement of two tracts of the spine - one governing sensations such as vibration and position sense, another governing motor function.  The course of disease progresses over months and can involve sensory loss involving the legs and hands and gait problems (the findings are a littel more complex and can be determined by a neurologist). Multiple Sclerosis can affect the same spinal symptoms and certainly cases of B12 deficiency have been reported that mimic MS, but generally there are distinguishing features such as time course (MS often relapses or worsens in a stepwise fashion rather than constant progression, MS has involvement of other systems e.g. cerebellum, characteristic imaging of the brain in MS, etc.).  Treatment would be B12 injections and evaluation should include why the deficiency is occuring (B12 is very rarely due to dietary reasons, generally due to poor absorption).  The longer the symptoms are present (e.g. many months to years), the less likely they will reverse with B12 supplementation, but B12 should still be given to prevent progression.  As for diagnosis, a blood test for a low B12 level is the best first step for diagnosis.  If high, B12 deficiency is not an issue.  There are borderline normal cases that may be indicative of B12 deficiency.  In these cases blood tests looking for Methylmalonic Acid and Homocysteine elevations can be sent for diagnosis.  Hope this was of help.