Background: Pseudoporphyria is a diagnosis that is used when porphyria-like clinical lesions arise in the setting of normal porphyrin levels. This condition was first described in the 1960s and was initially related to the use of certain antibiotic drugs. In 1985, pseudoporphyria was first attributed to the use of nonsteroidal antiinflammatory drugs (NSAIDs). Subsequently, a host of NSAIDs and other drugs have been found to elicit the same clinical entity. The exact mechanism by which certain drugs create clinical lesions resembling porphyria cutanea tarda or erythropoietic protoporphyria is still unknown. A phototoxic mechanism is hypothesized.
Objective: We describe six patients diagnosed with pseudoporphyria and detail the diagnostic tests leading to the eventual diagnosis.
Results: The patients ranged in age from 27 to 59 years and had a female:male predominance of 2:1. The offending NSAID was DayPro (oxaprozin) for three of the patients, Relafen (nabumetone) for two of the patients, and Aleve (naproxen) for one patient. For each patient, histology and immunofluorescence was either consistent with the diagnosis of porphyria cutanea tarda or nonspecific, while serum, stool, and urine porphyrins did not support that diagnosis. Withdrawal of the offending agent provided relief from the clinical symptoms for each patient. None of our patients were rechallenged with the putative offending drug. However, prolonged avoidance has provided a sustained remission from symptoms in all six patients.
Conclusions: Pseudoporphyria is a relatively rarely reported condition. Clinical suspicion with appropriate laboratory and histopathologic findings help to make this diagnosis, and exclude true porphyrias. Rechallenge with the offending drug to produce symptom relapse has been proposed to be helpful in confirming this diagnosis of exclusion. Since all 6 patients with drug-induced pseudoporphyria experienced resolution of their symptoms after discontinuing the offending agent, we propose that this clinical correlation alone is sufficient to confirm this diagnosis. Our observation of six new cases of NSAID-induced pseudoporphyria over a two-year interval suggests that this is not a rare entity.