A rare malignant skin infiltrate

A 9-month-old boy presented with urticaria-like cutaneous lesions. They appeared, for the first
time, at the age of 5 months. The first clinical diagnosis was a mast cell disorder or urticaria pigmentosa although antihistamines were not efficacious.
Previously, the child was treated for thrombocytopenic purpura. A complete work up and
systemic evaluation revealed severe thrombopenia. The bone marrow biopsy revealed no dyspoiesis in any of the cell lines. The final diagnosis was severe thrombocytopenic purpura in the context of an influenza-like syndrome. The treatment included systemic corticosteroids, sirolimus, rituximab, intravenous immunoglobulins and romiplostim. This immunosuppressive treatment led to a complete resolution of the skin lesions although recurrence was observed at treatment withdrawal.
The clinical examination evidenced brownish and erythematous granulomatous plaques of the
back, shoulders, face and thighs. A skin biopsy revealed a lymphoblastic infiltrate with blast cells
sparing the dermis. Immunohistochemistry revealed a positivity for CD45, PAX5n CD79a, CD43 and CD34. The morphology and immunohistochemical profile were in favor of a cutaneous localization of an acute B-type lymphoblastic leukemia versus a B-type lymphoblastic lymphoma.
The systemic workup showed no immunophenotyping abnormalities in the bone marrow and
no malignant cells in the central nervous system but a tumefaction of both testicles. The testicular
biopsy revealed an infiltration by a blastoid population expressing CD45, CD19 and CD34 whereas the cytogenetic revealed the presence of a partial 19p deletion and a MLL-AF10 rearrangement in 62% of nuclei.
The child was treated by chemotherapy following the diagnosis of aleukemic leukemia cutis
CD19+CD10-CD34+ CD20- with a testicular involvement and showed a good response.
Aleukemic leukemia cutis is defined as a cutaneous infiltration of leukemic cells in the absence
of both blood and bone marrow involvement. It is still not clear whether the malignant cells originate from the skin or spread from the bone marrow. The immature blast cells in the dermis and hypodermis clinically present as unspecific papules, nodules and plaques. Although rare and poorly characterized, recognition of this disease is important for early treatment. The management remains controversial.
A diagnostic workup should include a blood test, bone marrow studies, FISH and cytogenetics. The
treatment is similar as that for acute leukemia consisting in an induction and consolidation
chemotherapy.