A total of 21 patients were diagnosed with acute myelogenous leukemia (AML). Subclassifications of the leukemia were made in 10 patients, two having AML-M2, three having AML-M4, and five having AML-M5. Three patients had chronic myelogenous leukemia (CML) and six patients had chronic lymphocytic leukemia (CLL), three of them showing large cells that had been diagnosed as "transformation into non-Hodgkin lymphoma" by the referring hematologists. Four patients had acute lymphocytic leukemia (ALL).

Our patients presented themselves to us with widespread or individual lesions to equal proportions. Whereas cutaneous involvement in myelogenous leukemias took more often the form of an exanthem (60% versus 40%), lymphocytic leukemias were more often typified by individual lesions (30% versus 70%).

Lesions were small macules and papules in 20% of the cases, larger plaques in 53%, and nodules in 27 % of the cases. In two patients with AML, hemorrhagic bullae were present in the center of plaques. The color of lesions was livid in 60% of the patients and red in 40% of the patients. Two patients with chronic lymphocytic leukemia and one patient with AML had lesions on the scalp that were accompanied by alopecia. Only two patients complained about pruritus of lesions, and both of them had acute myelogenous leukemia.

Examples of clinical lesions in our patients are shown in Figures 1 –15.

A total of 55 specimens taken from our patients were reassessed. Infiltrates were sparse in 13% of the specimens, moderately dense in 52%, and dense in 35% of the specimens. In moderately dense and dense infiltrate, the pattern was nodular in a quarter of the specimens and diffuse in about half of the specimens. The subcutaneous fat was involved commonly, namely, in 63% of the cases, it most often being involvement in the form of a lobular panniculitis. When infiltrates were dense, they often gave the biopsy a rectangular shape similar to what has been described for biopsies of scleroderma adultorum Buschke. Infiltrates were centered around vessels in 71% of the specimens and they were adnexocentric in half of the specimens. In 46% of the specimens, cells of leukemia were found within the arrector pili muscle. Arrangement of cells splayed between collagen bundles in an indian file pattern was seen commonly whereas complete replacement of collagen fibres at least in foci was encountered in 17%.

In only nine specimens, cells of leukemia were seen in the epidermis, seven of them being taken from lesions of myelogenous leukemia in the skin, two being a from a patient with chronic myelogenous leukemia, and one being from a patient with chronic lymphocytic leukemia. A subepidermal grenz zone was spared in 61% of the cases.

Rarely, specimens showed signs of acuteness of a disease process such as edema of the papillary dermis, it being present in just four specimens. Extravasation of erythrocytes was seen in four specimens; in two of them, hemorrhage was accompanied by fibrin deposits in vessel walls and around them.

The size of cells was small in 14% of the specimens, intermediate in 46% of the cases, and large in 37% of the specimens. While cells were small in cases of chronic lymphocytic leukemia, they tended to be larger in acute lymphocytic leukemia and in both acute and chronic myelogenous leukemia. Whereas large cells in leukemias of lymphocytic differentiation consisted mainly of an enlarged nucleus, enlarged myelogenous cells were almost always rich in cytoplasm. In one third of myelogenous leukemias, cells resembled histiocytic cytomorphology. Sometimes, myeloblasts resembled enlarged plasma cells. Identification of subtypes of acute myelogenous leukemia was not possible based solely on infiltrates in the skin.

Infiltrates of myelogenous leukemia were monomorphous, except a few eosinophils being present in 4 specimens, and mature neutrophils being found in 5 specimens. In lymphocytic leukemia, infiltrates were predominantly monomorphous, too, but they tended to be pleomorphic in acute forms of lymphocytic leukemia. In chronic variants, infiltrates were not pleomorphic but exhibited irregular outlines and slight increase in size compared with normal lymphocytes. In two specimens taken from the site of a previous infection with varicella zoster viruses, granulomatous infiltrates were seen to intermingle with cells of chronic lymphocytic leukemia.

Mitotic figures were encountered in two thirds of the cases, but they were more commonly encountered in myelogenous variants and they were also more numerous. Mitotic figures ranged from 1 to 16 in a high-power field. Necrotic cells were seen in one third of all specimens, all of them coming from patients with myelogenous leukemia.

Squeeze artefacts, which are often mentioned to be a clue to malignant neoplastic infiltrates, were encountered in 17% of the specimens and made it difficult to assess cytopathologic details.

Patterns of leukemia cutis are pictured in Figures 16 –34.