Acute Intermittent Porphyria with a Secondary Porphyria Cutanea Tarda-like Biochemical Pattern in a Patient with Co-Morbid Human Immunodeficiency Virus Infection.

INTRODUCTION: Porphyrias are rare inherited disorders of heme synthesis caused by reduced activity of one of the eight enzymes in the pathway. When early precursors accumulate, acute hepatic porphyrias occur, which present as severe neurovisceral attacks. When later, light-sensitive porphyrins accumulate, they cause cutaneous forms with chronic photosensitivity, blistering and skin fragility. Although these patterns are usually distinct, acute, and cutaneous features may appear together. This may reflect two separate genetic defects, but more often occurs when oxidative stress, such as from iron overload, chronic infection, or drugs, secondarily inhibits the fifth enzyme, uroporphyrinogen decarboxylase. This creates a mixed porphyrin pattern in which the usual distinctions between acute and cutaneous porphyrias are blurred, making diagnosis challenging. CASE PRESENTATION: A 22-year-old woman living with human immunodeficiency virus (HIV) infection presented with recurrent abdominal pain during the luteal phase of menstruation, autonomic instability, and limb weakness that improved following heme arginate therapy. Urine porphobilinogen was markedly elevated, and hydroxymethylbilane synthase (HMBS) gene sequencing confirmed acute intermittent porphyria (AIP). However, her porphyrin studies also demonstrated pronounced urinary uroporphyrin elevation together with faecal isocoproporphyrins, a pattern characteristic of porphyria cutanea tarda (PCT). DISCUSSION: The findings are consistent with AIP complicated by secondary hepatic inhibition of uroporphyrinogen decarboxylase. In this patient, secondary uroporphyrinogen decarboxylase (UROD) inhibition was likely driven by persistent HIV viraemia, antiretroviral-associated hepatic oxidative stress, and chronic inflammatory activation which are well-recognised risk factors for acquired PCT-like biochemical patterns. CONCLUSION: This case demonstrates how co-morbidities can modify classical porphyria biochemical patterns and reinforces the need for integrated urine, plasma, and faecal interpretation, especially when biochemical profiles appear mixed. Clinically, patients living with HIV who have porphyria may benefit from closer monitoring for factors that increase liver stress, especially ongoing viraemia, hepatotoxic or porphyrinogenic drugs, alcohol use and iron overload. When virological control is poor, the risk of secondary UROD inhibition and mixed biochemical findings may increase. Regular review of HIV virological control, liver function, medication safety and porphyrin profiles may therefore help prevent recurrent attacks and reduce diagnostic confusion.