Conclusion
We reported the case as first presenting hyperpigmented macules and
patches on the face, neck and upper back after vitamin B12 ingestion.
The results of the patch test with the cobalt also showed hyperpigmented
reactions consistent with the clinical presentation suggesting the
diagnosis of systemic pigmented contact dermatitis resulting from oral
administration of cobalamin. The diagnosis was confirmed by
histopathological results of the positive patch test results
corresponding to the previous active lesions. We suggest investigating
systemic pigmented contact dermatitis in reaction to cobalt when
patients present unexplained hyperpigmented lesions.