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First described in 1961, photoonycholysis (PO) is a rare nail alteration that may result from drug intake, from topical aminolevulinate photodynamic therapy or from photosensitive conditions such as porphyria or pseudoporphyria. Spontaneous PO is rare. This review updates the numerous causes of PO and highlights some new ways producing this condition. Four different types of PO are clearly recognized without relationship with the responsible drug. An updated list of potential inducing drug is provided. Some practical points on PO have been raised. The inability to reproduce photoonycholysis experimentally should be emphasized, and the pathogenesis of PO still needs to be clarified., (© 2018 European Academy of Dermatology and Venereology.)

The porphyrias are uncommon diseases caused by enzymatic deficiencies in the heme pathway. In the 25 year period 1969-1994, the Department of Dermatology of the Hospital Clinic of Barcelona has been able to study 793 cases of porphyria (724 cases of PCT, 27 of EPP, 26 of PV, 5 of CEP, 5 of HEP, 5 of AIP, 1 of HCP). Homozygous expression of an enzymatic deficiency in the heme pathway produces severe disease. Commonly, clinical manifestations appear in the homozygous state (the autosomal recessive porphyrias). However, homozygous forms of autosomal dominant porphyrias may occur exceptionally. Moreover, there are cutaneous porphyrias whose clinical manifestations do not permit dermatologists to classify them clearly into one of the well-defined syndromes. These uncommon and atypical forms are difficult to recognize without biochemical and enzyme studies. The porphyrias have a wide clinico-biochemical spectrum, including a large proportion of well defined diseases. Nevertheless, atypical forms occur and may be difficult to evaluate. It is important to note the genetic heterogeneicity of porphyrias, which accounts for the varying phenotypic expression.

In contrast to Porphyria cutanea tarda (PCT), which is characterized by constant hepatic involvement, the liver seems to be unaltered in Porphyria variegata (PV). However, the authors have found microscopic alterations in the liver of 2 patients with PV (mild inflammation and fibrosis of the portal tracts and the presence of iron deposits in one of the cases). Although these changes could be attributed to other causes, the hypothesis of possible liver involvement in PV is not excluded.

Uroporphyrinogen decarboxylase levels were measured in haemolysed whole blood or fibroblasts from 3 unrelated patients with hepatoerythropoietic porphyria (HEP) and in 4 unrelated patients with familial porphyria cutanea tarda, a condition in which the enzyme is defective. In HEP patients enzyme activities were 7% of normal in erythrocytes and 8% of normal in cultured skin fibroblasts. All the features of HEP, including the characteristic accumulation of protoporphyrin in erythrocytes, are secondary to this enzyme defect. The father of 1 HEP patient was heterozygous for the same enzyme defect. He also had uroporphyrinuria and was therefore indistinguishable from patients with subclinical familial porphyria cutanea tarda. It is suggested that patients with HEP are homozygous for the gene that causes porphyria cutanea tarda.

A typical case of congenital erythropoietic porphyria in a 8 month old girl is reported (photosensitive blistering syndrome, hypertrichosis; erythrodontia; fluorescence of urine, teeth, erythrocytes and myeloblasts; splenomegaly; anaemia). Porphyrins, isomers I, were present in urine and blood. In faeces a porphyrin-X-like substance migrating as PX was detected; this porphyrin was finally identified as CP I unusually difficult to extract because of the presence of a banding and fluorescence quenching agent probably of exogenous origin. The usual methods are not always able to extract and to identify the faecal porphyrins.

The authors report two cases of cutaneous porphyria in children aged 6 and 9 respectively. The clinical and biochemical patterns were similar to those of porphyria cutanea tarda. The manifestations were drug-induced in both cases (by sulfonamides and griseofulvin in the first patient, and by hydantoin and benzodiazepine in the second). The clinical examination and the determination of porphyrins in the relatives showed no abnormalities. However, the study of the erythrocyte uroporphyrinogen decarboxylase showed 50 p. 100 reduced activity in the father and grandfather of the first patient, and in the second case's mother. Treatment with chloroquine (3 mg/kg/week) produced the total remission of both cases with no recurrences in 4 and 2 years respectively.