The photosensitive patient: could it be pellagra?

Abstract

Funding sources None. Conflicts of interest None declared. Generations of medical students have memorized the four ‘Ds’ of pellagra: dermatitis, diarrhoea, dementia and, less likely, death. Therefore, if a patient presents with the classic triad of a photoexposed dermatitis, diarrhoea and dementia, a diagnosis of pellagra can be readily made. Consider the more likely scenario for a dermatologist in which the patient lacks diarrhoea and dementia, instead presenting solely with photosensitivity and hyperpigmented lichenified plaques on photoexposed skin. Chronic actinic dermatitis (CAD), photoallergic contact dermatitis or phototoxicity might be considered in the differential diagnosis (Table 1). Yet, in a busy dermatology clinic, pellagra could be easily overlooked due to its rarity in developed nations. Pellagra is readily diagnosed with a serum niacin level, and easily treated with oral niacin supplementation. The difficulty lies in identifying those patients at risk of this rare disease. ... This month’s issue of the BJD includes an extensive review of pellagra contributed by Wan and colleagues1 Their thorough discussion provides the clinician with the salient features needed to arrive at a diagnosis. As is the case for other photosensitive disorders, historical clues are important in pellagra. As alcoholics are most likely to be affected in developed nations, serum niacin levels should be evaluated in a photosensitive patient who reports excessive alcohol intake.2 Pellagra may be secondary to anorexia, so the serum niacin should be assessed in a patient with concomitant presence of photosensitivity and history and signs of an eating disorder.3 Cutaneous signs of anorexia are multiple, but may include excessive lanugo hair, xerosis, telogen effluvium or knuckle calluses (Russell’s sign).4 Underlying gastrointestinal disorders such as coeliac disease or inflammatory bowel disease may predispose to pellagra due to malabsorption.5, 6 A photosensitive patient on predisposing medications, which include 5‐fluorouracil, isoniazid and azathioprine, must also be evaluated for the disease.7, 8