Porphyria cutanea tarda (PCT)

Meet the patient

A 54-year-old publican is sent by his GP for "blisters that will not heal" across the backs of his hands every summer. He blames gardening until his partner notices he tears at the lightest touch and fine dark hair has crept across his temples. Liver enzymes are mildly raised, ferritin is high, and a Wood's lamp held over his fresh urine glows pink-red.[1]

Two questions decide this consult, and they decide every PCT consult: is the porphyrin profile PCT? (the urine and plasma answer it within a day) and what is the liver trying to tell me? (HCV, alcohol, iron, oestrogen — screen them all). Hold those two questions and the management writes itself.[1][2]

A cutaneous porphyria that never attacks the nerves

PCT blisters the skin and never touches the nervous system — and that single line is the highest-yield fact in the topic. Abdominal pain, peripheral neuropathy, hyponatraemia, seizures or psychosis in a patient labelled "porphyria" is NOT a PCT flare; it is an acute hepatic porphyria (acute intermittent, variegate, or hereditary coproporphyria) — a different disease, a different emergency, and a different treatment.[1][4]

The reason is biochemical. PCT accumulates uroporphyrin and heptacarboxyl porphyrin — large porphyrin-ring molecules that settle in skin and absorb light. The acute porphyrias accumulate the small water-soluble neurotoxins ALA and porphobilinogen. Same pathway, opposite ends, opposite phenotypes: PCT is skin only; AIP, variegate and coproporphyria are nerves, sometimes with skin as well.[1][2]

The classic trap: a patient known to have "porphyria" who arrives with abdominal pain and dark urine is having an acute neurovisceral attack. Send urinary ALA and PBG (both raised) — never assume the PCT is acting up. PCT has no acute attack to treat, and giving haem arginate for "PCT" is both wrong and wasteful.[4]

Etymology for the viva: porphyria is from the Greek porphyuros*, "purple" — the colour of the concentrated urine and, historically, of the stained skin.* Cutanea tarda means "late cutaneous", because the skin disease appears in middle age, not in childhood.[4]

Read the skin like a dermatologist — the tetrad and the trap

Four signs on sun-exposed skin, found together, are PCT until disproved: skin fragility, tense vesicles and bullae, milia, and hypertrichosis — with hyperpigmentation completing the picture. The dorsal hands, forearms, V of the neck and face take the brunt, because that is where UV-A lands.[1]

The morphology is distinctive once you have seen it:[1]

• Fragility first — minor trauma such as towelling, gardening or washing-up shears the epidermis off the dorsal hands; the erosions are painless and heal with crusting, and this is often the earliest sign.
• Tense bullae — 0.5–3 cm fluid-filled blisters on the knuckles, dorsum, extensor forearms and pinna of the ear; they heal with milia and pigmentary change.
• Milia — 1–2 mm subepidermal keratin cysts, often the most stubborn residual lesion.
• Hypertrichosis — fine dark terminal hairs on the temples, lateral cheeks and upper lip; in women this is frequently the presenting complaint and a high-yield examiner sign.
• Hyperpigmentation — diffuse, mottled brown on sun-exposed skin.
• Sclerodermoid plaques — waxy indurated plaques on long-standing disease, with dermal fibrosis and no scleroderma-pattern antibodies.[1]

The mucosal rule that excludes PCT: the mucous membranes are spared and the Nikolsky sign is negative, because the split is at the basement membrane, not within the epidermis. Oral, conjunctival or genital bullae, or a positive Nikolsky, reopens the differential to pemphigus, mucous membrane pemphigoid or epidermolysis bullosa acquisita — not PCT.[1]

The screening bundle — six things every PCT patient gets tested for

The skin disease is the advertisement; the liver is the story. Every newly diagnosed PCT patient leaves the first visit with the same screen, because the treatment is to find and remove the precipitant, not merely to heal the skin.[1][2]

The cluster rule — three buckets: the bottle, the blood, the pill:[1]

• The bottle — alcohol: the cofactor that pairs with hepatitis C, especially in middle-aged men.
• The blood — hepatitis C, HIV, iron, dialysis: anti-HCV then HCV RNA (positive in 50 to 80 percent of PCT series); HIV; ferritin, transferrin saturation and HFE genotype (heterozygous C282Y in 30 to 50 percent of PCT patients); and renal failure, where porphyrin clearance falls.
• The pill — oestrogens: the oral contraceptive pill, HRT and tibolone, or oestrogen for prostate cancer; switch to a progesterone-only method.[1][2]

A PCT workup without these is incomplete, and "treat the skin, ignore the liver" is the recurring trainee error — because what kills the patient is the liver, not the blister.[1][3]

The 619–620 nm peak — one number splits the cutaneous porphyrias

Plasma fluorescence emission spectroscopy is the single highest-yield discriminator, and the number for PCT is 619–620 nm. Shine UV on the plasma and read where it glows: PCT 619–620 nm, variegate porphyria 626 nm, erythropoietic protoporphyria 634 nm. Three numbers, three diseases.[1][2]

At the bedside, Wood's lamp (UV-A 365 nm) over freshly voided urine is the 30-second test: pink-red fluorescence means massively raised urinary uroporphyrin and heptacarboxyl porphyrin — the PCT signature. Normal urine does not fluoresce, and ALA and PBG are normal, which is exactly why PCT has no neurovisceral attack.[1]

[1]

Three pillars — enzyme, iron, and light

PCT is UROD deficiency plus iron plus UV-A, and all three pillars are treatable. Knock out any one and the disease folds — which is the whole logic of phlebotomy and low-dose hydroxychloroquine.[3]

Pillar 1 — the enzyme. Uroporphyrinogen decarboxylase (UROD), the fifth step of haem synthesis, decarboxylates uroporphyrinogen to coproporphyrinogen. When hepatic UROD activity falls under 20 percent of normal, uroporphyrin and heptacarboxyl porphyrin accumulate, oxidise, and overflow into plasma and skin.[1][3]

Pillar 2 — the iron. Hepatic iron drives a Fenton-style oxidation that converts UROD substrate into a porphomethene — itself a competitive inhibitor of UROD. This vicious cycle is why the genetic deficiency stays silent until iron, alcohol or HCV tips it over, and why removing iron (phlebotomy) or mobilising porphyrin (low-dose hydroxychloroquine) reverses the disease.[3]

Pillar 3 — the light. Skin porphyrins absorb in the Soret band (400–410 nm, UV-A1) and generate singlet oxygen that wrecks the dermal–epidermal junction. Histology shows a subepidermal blister with festooning of the dermal papillae, PAS-positive perivascular deposits and caterpillar bodies in the roof — and direct immunofluorescence is negative, which separates PCT from the autoimmune blistering diseases.[1][4]

Sporadic or familial — the split that changes counselling, not treatment

Around 80 percent of PCT is sporadic (Type I, liver-only UROD deficiency, always precipitated); about 20 percent is familial (Type II, autosomal dominant UROD mutation at chromosome 1p34, all tissues). Subtyping rarely changes first-line treatment, but it changes what you tell the family.[1]

The laboratory split is erythrocyte UROD activity: reduced points to familial Type II; normal points to sporadic Type I or the rare Type III. Type II penetrance is under 10 percent unless a cofactor such as iron, HCV or alcohol is added, so most carriers never develop PCT — but their siblings and children deserve counselling once a proband is found.[1][3]

Hepatoerythropoietic porphyria (HEP) is the rare homozygous Type II: severe, mutilating photosensitivity from infancy with residual UROD activity under 10 percent, mimicking congenital erythropoietic porphyria. A child with bullae and photosensitivity is far more likely to have HEP, CEP or EPP than adult-pattern PCT.[1][4]

Investigations — three rings

Confirm the porphyrin profile, find the precipitant, and stage the liver — in that order.[1]

• Ring 1 — confirm PCT biochemically: a 24-hour urinary porphyrin profile (uroporphyrin and heptacarboxyl porphyrin markedly raised, ALA and PBG normal); plasma fluorescence emission peak at 619–620 nm; faecal isocoproporphyrin raised; erythrocyte UROD to subtype.
• Ring 2 — find the precipitant (the three-bucket screen): anti-HCV and HCV RNA, HBsAg, HIV, iron studies and transferrin saturation, HFE genotype, liver function tests, and eGFR.
• Ring 3 — stage the liver and watch for cancer: liver ultrasound with elastography at diagnosis; alpha-fetoprotein plus hepatic ultrasound 6-monthly if cirrhosis is present, 12-monthly otherwise; skin biopsy with PAS and direct immunofluorescence when the picture is equivocal.[1]

The biopsy is the tie-breaker when biochemistry is borderline: a subepidermal blister with festooning and caterpillar bodies, and a negative direct immunofluorescence, exclude the autoimmune blistering diseases and settle the diagnosis.[1][2]

Treatment — phlebotomy or low-dose hydroxychloroquine, never full-dose

Two first-line treatments, roughly equally effective, and one absolute rule: never give full-dose hydroxychloroquine. Choose by contraindication, not by preference.[1]

[1]

Therapeutic phlebotomy removes hepatic iron and reverses iron-mediated UROD inhibition. Withdraw 5–10 mL/kg (typically 450 mL) every 1–2 weeks until the ferritin approaches around 25 ng/mL, then maintenance if it rebounds; defer if the haemoglobin is under 12 g/dL.[1][3]

Low-dose hydroxychloroquine mobilises porphyrin from hepatic stores into the urine: 100 mg orally twice weekly (chloroquine 125 mg twice weekly is an acceptable substitute). It is the alternative first line when phlebotomy is contraindicated — anaemia, cardiac disease, poor venous access, or dialysis.[1][2]

[1] [1]

The named trap — the one the examiner is fishing for: full-dose hydroxychloroquine (200–400 mg daily) or chloroquine (250 mg daily) precipitates fulminant PCT hepatitis by acutely dumping hepatic porphyrin. The candidate who writes "200 mg daily" instead of "100 mg twice weekly" fails the stem. Low-dose has not caused hepatitis; full-dose has.[1][2][3]

[1]

Photoprotection must be lifelong, because the Soret band sits in UV-A and chemical sunscreens alone are insufficient — patients need opaque physical blockers (zinc oxide or titanium dioxide) plus UPF-rated clothing and window film. In pregnancy, phlebotomy is safe and hydroxychloroquine is contraindicated.[1][5]

Pseudoporphyria and the mimics — the face-off

Three look-alikes share the dorsal-hand blisters; the porphyrin profile and the story split them. Memorise the one-line discriminator for each, because the treatment of a mimic is the opposite of PCT.[1][5]

[1] [5]

The clincher for pseudoporphyria is the normal porphyrin profile in a patient whose skin looks exactly like PCT — usually on naproxen, sometimes on dialysis. Phlebotomy and hydroxychloroquine do nothing, because there is no porphyrin to remove; the only treatment is to withdraw the offending drug.[1][5]

How PCT patients come to harm — the preventable list

The skin rarely kills; the liver does. PCT mortality is dominated by chronic liver disease and hepatocellular carcinoma, with the risk raised 20 to 30-fold in established cirrhosis — which is why every cirrhotic PCT patient gets lifelong ultrasound plus alpha-fetoprotein surveillance.[3][4]

The preventable-harm list:[1][3]

• Fulminant hepatitis from full-dose hydroxychloroquine — the iatrogenic disaster; write "low-dose only" on the drug chart and in the clinic letter so no one re-prescribes 200 mg daily.
• Missed hepatocellular carcinoma — no surveillance ultrasound in a cirrhotic PCT patient who was owed one for life.
• Untreated hepatitis C — the largest reversible driver, now curable with direct-acting antivirals; remission after SVR is essentially permanent.
• Phlebotomy into anaemia — no haemoglobin check before a session in a borderline patient.
• Pseudoporphyria treated as PCT — phlebotomy and hydroxychloroquine for normal porphyrins, harming the patient and missing the naproxen.
• Acute porphyria missed as a "PCT flare" — abdominal pain and hyponatraemia attributed to the wrong disease, and haem arginate withheld.[1][4]

The mantra, and the mnemonic

[1] [2]

The mantra: blistering on the dorsal hands — check the liver and the porphyrins; phlebotomy or low-dose hydroxychloroquine, never full-dose.[1][2]

Ward-round test — four stems

Stem 1 — the publican from the top of the topic (answer)

The 54-year-old with summer blisters on his dorsal hands, raised liver enzymes, high ferritin and pink-red urinary fluorescence. Name the next two investigations and the first treatment. Model: This is classic PCT. Confirm with a 24-hour urinary porphyrin profile (uroporphyrin and heptacarboxyl porphyrin raised, ALA and PBG normal) and a plasma fluorescence emission scan (peak 619–620 nm). Screen the three buckets — HCV, alcohol, iron and HFE, oestrogens, HIV. First-line treatment is therapeutic phlebotomy to a ferritin around 25 ng/mL or low-dose hydroxychloroquine 100 mg twice weekly — never full-dose — plus lifelong photoprotection.[1][2]

Stem 2 — the abdominal pain that is not PCT (answer)

A patient known to have PCT is admitted with severe abdominal pain, vomiting and a sodium of 128 mmol/L. The registrar calls it a "PCT flare". What is the right call? Model: This is NOT PCT — PCT never causes neurovisceral attacks. This is an acute hepatic porphyria (AIP, variegate or coproporphyria) and a separate emergency. Send urinary ALA and PBG (both raised), manage the attack with analgesia, fluids, haem arginate and correction of hyponatraemia, and stop any precipitant drug. The diagnosis of PCT was never the whole story; screen for a second porphyria when skin and nerves coexist.[1][4]

Stem 3 — the dose the registrar almost wrote (answer)

The ward pharmacist queries a prescription for hydroxychloroquine 200 mg daily for newly diagnosed PCT. What is wrong, and what is correct? Model: 200–400 mg daily is the named trap — full-dose antimalarials precipitate fulminant PCT hepatitis by acutely dumping hepatic porphyrin. The correct dose is hydroxychloroquine 100 mg twice weekly (or chloroquine 125 mg twice weekly). Document "low-dose only" on the drug chart and in the clinic letter so it is never re-prescribed at full dose.[1][2][3]

Stem 4 — identical skin, normal porphyrins (answer)

A 60-year-old on naproxen for osteoarthritis has dorsal-hand blisters and milia indistinguishable from PCT, but the urinary and plasma porphyrins are normal. What is the diagnosis and the treatment? Model: This is pseudoporphyria — identical skin, normal porphyrins, classically from NSAIDs (naproxen) or dialysis. Phlebotomy and hydroxychloroquine do nothing because there is no porphyrin to remove. The treatment is to withdraw the naproxen and switch to a non-porphyrinogenic alternative; the skin usually settles over months.[1][5]

References

1. [1]Singal AK Porphyria cutanea tarda: Recent update Mol Genet Metab, 2019.PMID 30683557
2. [2]Sarkany RPE, Phillips JD The clinical management of porphyria cutanea tarda: An update Liver Int, 2024.PMID 38813949
3. [3]Leaf RK, Dickey AK Porphyria cutanea tarda: a unique iron-related disorder Hematology Am Soc Hematol Educ Program, 2024.PMID 39644053
4. [4]Frank J, Poblete-Gutiérrez P Porphyria cutanea tarda--when skin meets liver Best Pract Res Clin Gastroenterol, 2010.PMID 20955974
5. [5]Ayala F, Santoianni P Drug-induced cutaneous porphyria Clin Dermatol, 1993.PMID 7907270