Challenges in the identification of cobalamin-deficiency polyneuropathy.
BACKGROUND
Diagnosing cobalamin (Cbl) deficiency as a cause of polyneuropathy (PN) is problematic, as the frequency of both disorders increases with age, and serum Cbl levels can be difficult to interpret.


OBJECTIVE
To identify unique clinical or laboratory features among PN patients with Cbl deficiency and to examine the role of testing of serum metabolite levels in the identification of Cbl deficiency.


METHODS
Cohort survey comparing patients with Cbl deficiency and cryptogenic PN identified during a 2-year period. Cobalamin deficiency was diagnosed using low serum Cbl levels or elevated serum methylmalonic acid or homocysteine levels.


METHODS
Academic neuromuscular clinic.


RESULTS
Of 324 PN patients, 27 were diagnosed as having Cbl deficiency. Twelve had Cbl levels within the normal range, but elevated serum metabolite levels. Compared with patients with cryptogenic sensory/sensorimotor PN, those with Cbl deficiency were more likely to have concomitant involvement of the upper and lower extremities and experience symptom onset in the hands and a sudden onset of symptoms (P<.005). These differences were seen regardless of whether Cbl deficiency was defined using low Cbl levels or elevated serum metabolite levels. Autoimmune pernicious anemia was identified in 6 (50%) of 12 Cbl-deficient patients with normal serum Cbl levels. The patients with PN and Cbl deficiency showed little objective improvement after parenteral replacement therapy; however, progression occurred less often in these patients compared with those with cryptogenic sensory/sensorimotor PN (P =.02).


CONCLUSIONS
This study highlights the challenges of proving that Cbl deficiency is the cause for PN and identifies clinical features that suggest Cbl-deficiency PN. Testing of serum metabolite levels may identify Cbl deficiency in some patients with normal serum Cbl levels.
Saperstein
David S
DS
Department of Neurology, University of Kansas Medical Center, Kansas City 66160, USA. dsaperstein@kumc.edu
Wolfe
Gil I
GI
Gronseth
Gary S
GS
Nations
Sharon P
SP
Herbelin
Laura L
LL
Bryan
Wilson W
WW
Barohn
Richard J
RJ
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000752:Anemia, Pernicious / Q000097:blood / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D006710:Homocysteine / Q000097:blood; D006801:Humans; D008297:Male; D008764:Methylmalonic Acid / Q000097:blood; D008875:Middle Aged; D011115:Polyneuropathies / Q000175:diagnosis* / Q000453:epidemiology / Q000209:etiology*; D014806:Vitamin B 12 Deficiency / Q000097:blood / Q000150:complications* / Q000453:epidemiology
D006710:Homocysteine; D008764:Methylmalonic Acid