Unexpected presentation of acute porphyria

Correspondence to Dr Adeline Serena Ee Ling Lam; [email protected]

Background

Porphyrias are a group of rare inherited metabolic diseases characterised by the catalytic defect of one in eight enzymes involved in haem biosynthetic pathway.^1–3 Porphyrias are broadly classified into acute porphyrias and cutaneous porphyrias based on their clinical presentation. Acute porphyrias are characterised by potentially life-threatening acute attack of neurovisceral manifestations, for example, abdominal pain, convulsion, autonomic hyperactivity, peripheral neuropathy and psychiatric symptoms. Of all acute porphyrias, acute intermittent porphyria (AIP) is by far the most common and only presents with acute attack. AIP more commonly affects women and is rare before puberty and after menopause, with occurrence peaking in the third and fourth decades.^{1 2}

Our current understanding of the epidemiology of porphyria is largely contributed by European studies.⁴ Cases in Asia are generally limited to a small number of case reports and series except Japan. Japan had the largest cohort of 827 cases of porphyria since the first diagnosis of porphyria in 1920, of which 330 cases were acute porphyria.⁵ In the same study, the author concluded that the incidence of porphyria in Japan is consistent with that reported in Europe. There is an increasing recognition of the incidence of acute porphyria, especially AIP and its associated genotypes, in China. Of note, there is yet a population-wide epidemiological study in China, but it is suggested that the actual incidence of acute porphyria may not be as rare as previously estimated.⁶

Acute porphyrias are rarely reported in Southeast Asia. There were only two cases of acute porphyria reported in Singapore since 1983,^{7 8} while Malaysia has seen three cases of acute porphyria since 1978, with the latest case being reported in 2019.^9–11 Thailand observed six cases of acute porphyria since 1973.^12–14 These case reports are summarised in table 1.

Table 1

Summary of acute porphyria case reports from Malaysia, Singapore and Thailand

No	Patient details (as available)/source	Symptoms and signs on admission	Significant laboratory finding	Diagnostic test	Final diagnosis	Progress and outcome
1*	Thailand, 1973	–	–	–	AIP	–
2	Malaysia, 1978, 23-year old woman/Chong et al9	Vomiting, abdominal pain, constipation, seizure, hypertension, tachycardia, dark urine	Sodium, 100 mmol/L	Positive Watson-Schwartz test†	Acute porphyria