Hairy Cell Leukaemia with Leucocytosis: A Rare Case Report with Review of Literature

Hairy Cell Leukaemia (HCL) is an uncommon disease that accounts for 2% of all lymphoid leukaemias. It is characterised by the proliferation of lymphoid cells with abundant cytoplasm with circumferential fine hairy projections involving the peripheral blood, Bone Marrow (BM), and expanding splenic red pulp. A 50-year-old male presented to the medicine outpatient department with a history of weakness and breathlessness for three days hampering his daily chores. There was no history of any other chronic illness. The review of the peripheral blood smear demonstrated marked leucocytosis showing lymphocytosis. Some of these lymphocytes displayed hairy cytoplasmic projections. Red blood cells showed a dimorphic blood picture. BM aspiration was performed which was insufficient for opinion. BM cell block revealed mononuclear cells with perinuclear clearing giving a fried egg appearance. BM biopsy revealed a predominance of mononuclear cells with round nuclei suggestive of lymphoid cells. These cells showed an interstitial pattern of infiltration. Clear zones are seen around the nucleus (fried egg appearance). A diagnosis of lymphoproliferative disorder with the closest resemblance to HCL was made which was confirmed on Flow Cytometry (FCM) with these lymphoid cells showing positivity for CD45, CD20, CD25, and CD123. HCL with leukocytosis is relatively a rare presentation. Immunophenotyping plays a crucial role in making its diagnosis.