Among myeloproliferative diseases, “unclassifiable” is also indicated. This category includes diseases that have all the features of myeloproliferative, but without a sufficient number of signs that can be attributed to any specific nosological unit. The merit of the authors of the classification is in strict caution against making a diagnosis of myeloproliferative unclassifiable disease in those cases when all modern diagnostic methods that make it possible to accurately identify the diagnosis were not used. It is indicated that most often after some time, in cases initially diagnosed as unclassifiable, certain features of true polycythemia, or chronic idiopathic myelofibrosis, or essential thrombocythemia, appear.
In chronic myeloproliferative / myelodysplastic diseases, there are features of delayed maturation and dysplasia in any of the hematopoietic lines and / or ineffectiveness of hematopoiesis in this line. It seems to us absolutely correct to assign chronic myelomonocytic leukemia to this group, which was previously considered as one of the variants of myelodysplastic syndromes and which certainly has features of both myeloproliferative and myelodysplastic diseases. There is no doubt that the classification of juvenile myelomonocytic leukemia to this category is correct.
This group also contains a rare disease – atypical chronic myeloid leukemia, for which the term “subacute myeloid leukemia” was used long ago. The disease is characterized by hyperleukocytosis, the presence of young forms of granulocytes in the blood (promyelocytes, myelocytes, metamyelocytes), the absence of basophilia and the presence of signs of dysplasia in the cells of the granulocytic germ and sometimes also in the cells of the erythroid and / or megakaryocytic germ hemopoiesis. Chromosomal aberrations are common, but there are no specific ones among them, in particular, Ph (BCR-ABL) is not detected. The level of alkaline phosphatase in neutrophils can be any. Most likely, pathogenetic mechanisms of the development of this disease will be established in the future and it will be identified more specifically.
In this category also has unclassifiable myelodysplastic / myeloproliferative disease, which the authors designated as a disease having both laboratory features of one embodiment myelodysplastic syndrome and myeloproliferative process, such as thrombocytosis, or simultaneously features myeloproliferative and myelodysplastic processes which can not be attributed to any specific category . Chromosomal aberrations can occur, but are not specific to a particular disease.
It should be recognized that almost every hematologist meets with diseases that can not be attributed to any particular category. The merit of the authors of the classification is that they have designated this provision, although the term “unclassifiable” disease, even assigned to a specific group, cannot fully satisfy. It reflects the current state of science and the obscurity of the biological mechanisms underlying some clinical and morphological syndromes.