Vitamin B12 deficiency common in primary hypothyroidism.

Objective: To assess the prevalence and clinical features of B12 deficiency in hypothyroid patients and to evaluate clinical response in symptoms to B12 replacement therapy.

Methods: One hundred and sixteen hypothyroid patients from our endocrine clinic were evaluated for signs and symptoms of vitamin B12 deficiency. Laboratory parameters including Haemoglobin (Hb), MCV, Vitamin B12 levels and presence of anti thyroid antibodies were analyzed. Patients with low B12 levels were treated with parenteral intramuscular vitamin B12 monthly, and monitored for improvement of symptoms.

Results: A total of 116 patients (95 females and 21 males) were evaluated. Forty six (39.6%) hypothyroid patients had low vitamin B12 levels. Males and females had the same prevalence of B12 deficiency. Generalized weakness, impaired memory, depression, numbness and decreased reflexes were more frequently noted in B12 deficient patients, but failed to achieve statistical significance when compared with B12 sufficient patients. The mean Hb in B12 deficient group was 11.9 +/- 1.6 mg/dl and 12.4 +/- 1.7 mg/dl in the B12 sufficient group, however the mean MCV did not differ in the two groups. Patients with B12 deficiency did not have a higher prevalence of anaemia. Thyroid antibodies were checked in half the patients and 67% had positive titers for anti thyroid antibodies. Prevalence of vitamin B12 deficiency did not differ in patients with positive antibodies (43.2%) compared to those with negative antibodies (38.9%) (p= 0.759). Twenty four hypothyroid patients with B12 deficiency received intramuscular vitamin B12 injections monthly and improvement in symptoms was noted in 58.3% of these subjects. Additionally, 21 subjects complained of symptoms consistent with B12 deficiency but who had normal range B12, levels and were prescribed monthly B12 injections and 8 (40%) had good subjective clinical response at 6 months.

Conclusions: There is a high (approx 40%) prevalence of B12 deficiency in hypothyroid patients. Traditional symptoms are not a good guide to determining presence of B12 deficiency. Screening for vitamin B12 levels should be undertaken in all hypothyroid patients, irrespective of their thyroid antibody status. Replacement of B12 leads to improvement in symptoms, although a placebo effect cannot be excluded, as a number of patients without B12 deficiency also appeared to respond to B12, administration.