RESUMO
Two cases of tyrosinaemia type II, an extremely rare inborn error of metabolism with a deficiency in tyrosine aminotransferase, are reported. Our patients presented with elevated tyrosinaemia, tender patchy palmoplantar keratoderma and pseudoherpetic keratitis, characteristic of the syndrome, but were not mentally retarded. Etretinate relieved pain, eye and skin lesions rapidly, and prevented recurrences, without lowering serum tyrosine. Skin lesions contain crystal-like intractyoplasmic inclusions of tyrosine. An acidic type I Keratine 64kd, which is present in palmoplantar skin only, may be altered and/or provide a more favourable terrain for crystallisation. Etretinate decreases this type of keratin, which explains the long term benefit of maintenance therapy. In addition, its rapid action in alleviating pain may be ascribed to competition with tyrosine at the cell receptor level, thus increasing the threshold for crystallisation and/or clinical manifestations