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In July 1985, a 43‐year‐old man was found to have polycythaemia vera. The peripheral blood counts were white cell count 14.15×109/l (neutrophils 80%, lymphocytes 14%, monocytes 5%, eosinophils 1%), haemoglobin concentration 24.8 g/dl, haematocrit 0.7, red cell count 8.15×1012/l (neither anisocytosis nor poikilocytosis nor tear‐drop poikilocytosis were observed), platelets 234×109/l. As only the erythroid lineage was affected significantly, he was treated with isovolaemic phlebotomy until April 2004. In May 2004, the patient suddenly developed a spastic paraplegia. Nuclear magnetic resonance imaging showed a posterior extradural tumour extending from T3 to T11 (fig 1A, BB).). The lesion expanded into the vertebral canal, inducing spinal cord compression. The occurrence of either a second neoplasm or a myeloid sarcoma (rare but possible during the clinical course of polycythaemia vera) was considered in the differential diagnosis. After thoracic laminectomy (from T2 to T11) and removal of the extradural lesion, all the symptoms resolved promptly and completely. A morphological and immunohistochemical analysis was then carried out to establish the diagnosis and to decide on the treatment. The tumour was composed of a heterogeneous cellular population resembling physiological haematopoiesis in all its components (fig 1G1G).). The immunohistochemical analysis showed that the mass was composed of a cellular population resembling that of normal erythropoiesis and granulopoiesis, with cells at all stages of maturation. Glycophorin staining showed the erythroid population (fig 1C1C)) and myeloperoxidase, and linker of activation of T cells showed cells of the granulocytic series and megakaryoblasts/megakaryocytes (fig 1D, 1E1E),), respectively. The number of blast cells, evaluated by CD34 staining, was not increased (<5%; fig 1F1F),), thus excluding the possibility of myeloid sarcoma with partial maturation.
The occurrence of extramedullary haemopoiesis is well known in cases of primary or secondary myelofibrosis. However, this phenomenon is extremely rare in association with other haematological diseases, such as inherited anaemias (especially thalassaemia) and chronic myeloproliferative disorders without evolution to myelofibrosis. Our case has unique and unexpected features. It should be underlined that immunohistochemistry was essential for a correct diagnosis, particularly for excluding myeloid sarcoma, which would have required intensive postoperative chemotherapy.
At the time of writing, after a follow‐up of 13 months, the patient is well, with no neurological signs or symptoms. The peripheral blood counts were white cells 9.76×109/l (neutrophils 78%, lymphocytes 16%, monocytes 4%, eosinophils 2%), haemoglobin concentration 13.2 g/dl, haematocrit 49.3%, platelets 179×109/l. His current treatment consists of isovolaemic phlebotomy and hydroxycarbamide (hydroxyurea), given to prevent possible new extramedullary haemopoiesis.
Funding: This work was supported in part by COFIN 2002–2003 (MB), AIRC, AIL Bologna, Ateneo 60% (MB and SAP), and Fondazione del Monte di Bologna e Ravenna grants. PPP was supported by Italian–American Cancer Foundation and AIRC (Leonino Fontana e Maria Lionello fellowship).
Competing interests: None declared.