Cutaneous lesions and vitamin B12 deficiency

The picture shows hyperpigmentation on both feet. A 34-year-old woman complained of skin lesions that had developed on both her feet over the past 1.5 months. She was a nonvegetarian. She was under the care of an endocrinologist for hyperthyroidism and was using a 7.5-mg dose of carbimazole daily. On examination, she had non-itchy, hyperpigmented macular lesions predominantly on the dorsum of the middle phalanges of the toes of both feet. There was no rash or dermatitis preceding the onset of hyperpigmentation. This was her only physical sign. Clinical examination was otherwise unremarkable. There were no clinical features suggestive of autoimmune disorders. The vitamin B12 level was 113 pmol/L (normal range 132 to 857 pmol/L). The full blood count and mean corpuscular volume were within normal limits (normal range 80 to 97 fL). As there was no other cause for the hyperpigmentation except for a low serum vitamin B12 level, she was started on intramuscular injections of 1000 mcg of vitamin B12 followed by a vitamin B complex (vitamins B1, B6, and B12) tablet daily. The vitamin B12 level after treatment was 300 pmol/L. The hyperpigmented lesions improved within 2 weeks of starting treatment.