Abstract
We welcome the opportunity to respond to Pfafflin's letter, which questions the diagnosis of AIP in our case report. The urine and faecal samples used for initial investigations were collected 11 days after the acute attack. In acute intermittent porphyria (AIP), urine porphobilinogen (PBG) excretion is usually greater than 10 times the upper limit of the normal during, and for at least one week after, an attack, but a five-fold increase after the early stage remains consistent with AIP;
1
Increased urinary porphyrins, mainly uroporphyrin but also coproporphyrin, are usually found in AIP;
1
Erythrocyte PBG deaminase is not an essential measurement for the diagnosis of AIP, and normal activity does not exclude the diagnosis;
1
Faecal coproporphyrin is typically normal or slightly elevated, as found in our case; Specific treatment for AIP with glucose or haemin was not used because the diagnosis was not made until the patient had recovered from the acute attack; The R173W mutation is a well-recognized cause of AIP
2
and exons 10, 12 and 14 are involved in 35% of cases;
3
The patient's liver and kidney function tests and haematological profile were normal, excluding some secondary disorders of porphyrin metabolism.
We agree that the initial biochemical studies alone do not enable confident identification of the type of porphyria and, in our paper, we acknowledge the limitations of the biochemical methods available to us at the time. It was for this reason that the initial provisional diagnosis was acute hepatic porphyria – a term that encompasses AIP, variegate porphyria and hereditary coproporphyria. The patient did not exhibit any porphyria cutanea tarda-like skin lesions. It was the combination of the biochemical data together with a previously recognized pathological mutation, confirmed in a detailed family study, that allowed the final diagnosis of AIP.