Myeloma with Xanthoderma Due to an IgGλMonoclonal Anti-Flavin Antibody

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Abstract
When yellow skin and yellow hair developed in an elderly patient with multiple myeloma, we ruled out the usual causes of such pigmentation but identified a monoclonal LgGλ (LgGGar) with anti-flavin antibody activity. Purified LgGGar was brightyellow, and the acid-dissociated chromophore was identified as riboflavin by chromatography and absorption spectroscopy. Native LgGGar contained 1.45 moles of flavin per mole of IgG, and increased to 2 moles with addition of riboflavin to saturation. The flavin was localized to the Fab fragment and was bound to LgGGar with high affinity. LgGGar showed strongest affinities for riboflavin, flavin mononucleotide and flavin adenine dinucleotide, and lower affinities for dinitrophenyl derivatives and naphthoquinone. The demonstration of hapten bound to the circulating monoclonal immunoglobulin in this case suggests the possibility of bound but colorless haptens on other myeloma proteins as well as on normal immunoglobulins (N Engl J Med 294:177–183, 1976)