6.2.2 Porphyria Cutanea Tarda
Grading & Level of Importance: B
The disease typically manifests around the age 40-70 years. It is a rare condition, with less than 1% of the general population affected. However, it accounts for around 1/3 of all cases of porphyria. Males are twice as likely as women to suffer from this disease.
Porphyria cutanea tarda is a disease caused by a chronic disturbance in hepatic porphyrin synthesis, resulting in accumulation of photosensitive porphyrins in the skin and other organs.
Aetiology & Pathogenesis
The aetiology is genetic and may be inherited in an autosomal dominant fashion, or acquired. It is characterised by a deficiency in uroporphyrinogen-III decarboxylase. External triggers include alcohol, medications (antifungals, analgesics, barbiturates, contraceptive pill, chloroquine and many others) and poisoning with heavy metals (such as lead and arsenic). Liver infections such as HIV and/or hepatitis C may cause or unmask the disease.
Signs & Symptoms
Blistering occurs in light-exposed areas and with minimal trauma (e.g. on the face and backs of the hands, bolded scalp). As the blisters are fragile and easily de-roofed, commonly only erosions are seen. Skin frequently heals with the appearance of milia and atrophy. Hypertrichosis variably occurs on the cheeks and temples. Pseudoscleroderma is rarely seen. Some patients notice that their urine is discoloured.
Type 1 (exogenous cause) and type 2 (genetic).
Laboratory & other workups
Laboratory tests are essential for a firm diagnosis, as there can be considerable clinical overlap between different forms of porphyria.
Blood: elevated liver enzymes are usually seen.
Urine: levels of uroporphyrins (I > III) may be measured to confirm the clinical diagnosis.
The features on biopsy are not specific but may include subepidermal blisters, thickened basement membrane and thickened vessels (PAS-stain). Biopsy may be helpful to exclude other causes of blistering (e.g. autoimmune blistering conditions).
The course is often chronic. It is important to eliminate as many trigger factors as possible (even in type 2) e.g. reduction of alcohol intake, avoidance of prohibited medications etc. Lists of safe medications are available online.
Complications include cosmetically troublesome hypertrichosis and delayed wound healing, pseudoscleroderma causing reduced function/mobility.
Whilst a clinical diagnosis may be possible in classical cases, the diagnosis should always be confirmed via laboratory tests.
The differential diagnosis includes other blistering disorders and pseudoporphyrias. Erythropoietic protoporphyria, which however never shows blistering.
Prevention & Therapy
Sun avoidance is important with the use of topical sunscreens (SPF >30).
Avoidance of triggers (such as alcohol, hepatotoxic medications) can be very helpful clinically. If iron stores are very high, regular phlebotomy may be employed. Chloroquine given in very low doses twice weekly may be an effective treatment.
- Statement 1 A positive Nikolski sign is typical for porphyria cutanea tarda
- This 60-year-old wine dealer complains of sores and bruises on the backs of his hands. What tests are indicated?
- This 30-year-old beautician with known hepatitis C infection complains of increased facial hair requiring epilation and an eczema on the backs of her hands. What is the most likely diagnosis?
- Statement 1 On Wood light examination, the urine in porphyria cutanea tarda fluoresces red-orange.
- Which statement about porphyria cutanea tarda is false?
- Which additional studies are appropriate in porphyria cutanea tarda?
- Which of these treatments are appropriate for porphyria cutanea tarda?
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