Diagnostic Approach to Porphyria Cutanea Tarda (PCT)
The diagnosis of Porphyria Cutanea Tarda requires biochemical testing showing elevated urinary porphyrins, particularly uro- and heptacarboxyl porphyrins, as the clinical features alone are not specific enough to establish the diagnosis. 1
Initial Evaluation
- Plasma fluorescence scanning is recommended as a first-line analysis for patients with cutaneous symptoms suggestive of PCT 1
- Patient history should specifically assess for known PCT risk factors, including alcohol consumption, hepatitis C virus infection, iron overload, and hereditary hemochromatosis 1
- Visual examination of urine can provide valuable diagnostic clues - urine of PCT patients appears red to brown in natural light and pink to red in fluorescent light 2
Biochemical Testing
- Fractionation of porphyrins in urine is the standard diagnostic approach for PCT 1
- PCT is characterized by elevated uro- and heptacarboxyl porphyrins in urine 1
- Samples must be protected from light to avoid falsely low results 1
- In fecal samples, hepta-, penta-, and isocoproporphyrins predominate 1
- Isocoproporphyrin in feces is a characteristic finding in PCT 3
- For patients with kidney failure, fractionation of porphyrins in plasma may facilitate diagnosis 1
Confirmatory Testing
- Measurement of uroporphyrinogen decarboxylase (UROD) activity in erythrocytes helps differentiate between sporadic (type I) and familial (type II) PCT 1
- Genetic testing for UROD gene mutations should be considered to distinguish between sporadic (type I) and familial (type II) PCT 1
- Liver biochemical profile should be assessed as mild abnormalities are common in PCT 4
- Screening for hepatocellular carcinoma using ultrasound examination is recommended, especially in patients with cirrhosis or advanced fibrosis 4
Diagnostic Pitfalls to Avoid
- Relying solely on clinical presentation without biochemical confirmation 1
- Using only total urine porphyrin tests without fractionation 1
- Failing to protect samples from light exposure, which can lead to falsely low results 1
- Not considering pseudoporphyria in the differential diagnosis, which can mimic PCT clinically but lacks the characteristic biochemical findings 1
- Overlooking the need to screen for hepatitis C and possibly B, particularly in patients less than 30 years old with extremely high liver transaminase levels 2
Additional Considerations
- Skin biopsy of a bullous lesion may be useful to rule out other diseases with similar presentations 2
- Even in patients with familial PCT (type II), the disease phenotype requires hepatic UROD deficiency to below 20% of normal, so other susceptibility factors must be present 4
- Patients with PCT should be evaluated for liver disease, as advanced fibrosis and cirrhosis with hepatocellular carcinoma can occasionally develop 4
- Long-term follow-up is needed in all patients to monitor for relapse, especially when susceptibility factors are not adequately controlled 5