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The case involves a 75-year-old man with incidentally detected isolated thrombocytopenia and relative lymphocytosis. Peripheral smear suggested hairy cells, while flow cytometry confirmed classical HCL plus a small CLL-like monoclonal B-cell clone. Abdominal CT revealed a renal lesion suspicious for carcinoma, prompting coordinated urological management and surveillance for both conditions.",{"@graph":69,"@context":123},[70,84,106],{"@type":71,"itemListElement":72},"BreadcrumbList",[73,77,79,82],{"item":74,"name":75,"@type":76,"position":8},"https://docshare.wps.com","Home","ListItem",{"item":78,"name":9,"@type":76,"position":14},"https://docshare.wps.com/document/",{"item":80,"name":35,"@type":76,"position":81},"https://docshare.wps.com/document/healthcare/",3,{"item":83,"name":65,"@type":76,"position":19},"https://docshare.wps.com/document/hidden-in-plain-sight-unmasking-hairy-cell-leukemia-through-structured-clinical-reasoning/437602/",{"url":83,"name":65,"@type":85,"image":86,"author":91,"headline":65,"publisher":94,"fileFormat":97,"inLanguage":63,"description":67,"dateModified":98,"datePublished":99,"encodingFormat":97,"isAccessibleForFree":100,"interactionStatistic":101},"DigitalDocument",{"url":87,"@type":88,"width":89,"height":90},"https://docshare.wps.com/thumbnails/hidden-in-plain-sight-unmasking-hairy-cell-leukemia-through-structured-clinical-reasoning/437602.png","ImageObject",300,407,{"name":92,"@type":93},"4398046744996","Person",{"url":74,"name":95,"@type":96},"DocShare","Organization","application/pdf","2026-11-01","2026-09-29",true,{"@type":102,"interactionType":103,"userInteractionCount":105},"InteractionCounter",{"@type":104},"ViewAction",14,{"@type":107,"mainEntity":108},"FAQPage",[109,115,119],{"name":110,"@type":111,"acceptedAnswer":112},"Why was the hairy cell leukemia diagnosis delayed initially?","Question",{"text":113,"@type":114},"HCL often presents with subtle, nonspecific laboratory abnormalities. In this case, isolated thrombocytopenia and relative lymphocytosis were incidental, which can be mistaken for benign or age-related changes.","Answer",{"name":116,"@type":111,"acceptedAnswer":117},"What tests supported the diagnosis of classical HCL in this case?",{"text":118,"@type":114},"Peripheral blood smear showed lymphoid cells with cytoplasmic projections suggestive of hairy cells. Flow cytometry then confirmed a dominant clonal population consistent with classical HCL.",{"name":120,"@type":111,"acceptedAnswer":121},"How did the renal lesion influence clinical management?",{"text":122,"@type":114},"CT imaging found a renal lesion suspicious for carcinoma. This incidental finding led to prioritizing urological intervention and highlighted multidisciplinary coordination when concurrent malignancies are present.","https://schema.org",{"og:url":83,"og:type":125,"og:title":65,"og:site_name":95,"og:description":67},"article",{"robots":127,"canonical":83},"index,follow",{"doc_id":129,"site_id":62},437602,1790871722,{"code":4,"msg":5,"data":132},{"doc_id":129,"user_id":133,"nickname":92,"user_avatar":66,"doc_module":4,"category_id":34,"category_name":35,"doc_title":65,"doc_description":67,"doc_content":134,"file_id":135,"file_url":136,"file_type":137,"file_size":138,"view_count":105,"is_deleted":4,"is_public":8,"is_downloadable":8,"audit_status":8,"page_count":24,"language":139,"language_code":63,"site_id":62,"html_lang":63,"table_of_contents":140,"faqs":141,"seo_title":142,"seo_description":67,"update_tm":143,"read_time":144,"preview_page_count":4},4398046744996,"Review began 12/12/2025  \nReview ended 12/23/2025  \nPublished 01/05/2026  \n© Copyright 2026  \nVeiga et al. This is an open access article distributed under the terms of the Creative Commons Attribution License CC-BY 4.0. , which permits unrestricted use , distribution , and reproduction in any medium , provided the original author and source are credited.  \nDOI: 10.7759/cureus.100803  \nOpen Access Case Report  \nHidden in Plain Sight: Unmasking Hairy Cell Leukemia Through Structured Clinical Reasoning  \nLuís D. Veiga 1, Inês F. Teixeira 2 , Joana B. Vaz 2 , Paula Leite 2 , Joana Gonçalves 1  \n1. Internal Medicine, ULS Póvoa de Varzim/Vila do Conde, Póvoa de Varzim, PRT 2. Clinical Pathology, ULS Póvoa de Varzim/Vila do Conde, Póvoa de Varzim, PRT  \nCorresponding author: Luís D. Veiga, [lveiga@ulspvvc.min-saude.pt](lveiga@ulspvvc.min-saude.pt)  \nAbstract  \nHairy cell leukemia (HCL) is a rare, indolent B-cell neoplasm that often presents with nonspecific laboratory findings, which can delay diagnosis. We report the case of a 75-year-old male with incidentally detected isolated thrombocytopenia and relative lymphocytosis. Peripheral blood smear showed lymphoid cells with cytoplasmic projections suggestive of hairy cells. Flow cytometry confirmed a dominant clonal population consistent with classical HCL, along with a small CD5+/CD23+ monoclonal B-cell population compatible with a chronic lymphocytic leukemia-like clone. Abdominal CT also revealed a renal lesion suspicious for carcinoma. This incidental finding led to the prioritization of urological intervention, illustrating how multidisciplinary management is coordinated when concurrent malignancies are present. The patient remains asymptomatic and under active surveillance for both conditions. Subtle hematologic abnormalities may indicate early stages of HCL, and internists play a crucial role in recognizing these early signs and initiating targeted diagnostic evaluation.  \nCategories: Hematology, Internal Medicine  \nKeywords: clinical pathology, cytopenia, diagnostic reasoning, differential diagnosis, hairy cell leukemia, indolent bcell neoplasm, multidisciplinary care, peripheral smear, thrombocytopenia  \nIntroduction  \nHairy cell leukemia (HCL) is a rare, mature B-cell lymphoproliferative disorder accounting for approximately 2% of all leukemias [1] . It is characterized by small-to-medium-sized B lymphocytes with fine cytoplasmic projections (“hairy cells”) and a distinctive immunophenotype typically showing bright CD20 expression along with CD11c, CD103, and CD123 [2] . The near-universal presence of the BRAF V600E mutation in classical HCL has further refined diagnostic classification and guided targeted therapeutic strategies [2] . Despite these well-defined features, HCL often presents insidiously. Cytopenias-sometimes isolated-and subtle or incidental abnormalities on routine blood tests may be the earliest signs, leading to frequent misinterpretation as benign or age-related changes [3,4] .  \nMaintaining a high index of diagnostic suspicion in the setting of unexplained hematologic abnormalities is therefore essential. Peripheral blood smear evaluation and immunophenotyping remain crucial for early recognition, while timely referral to hematology facilitates appropriate surveillance and clinical decisionmaking [2,5] . This report underscores the pivotal role of internal medicine in detecting rare hematologic malignancies such as HCL, which may be masked by seemingly minor laboratory abnormalities like isolated thrombocytopenia and relative lymphocytosis, thereby enabling prompt diagnostic clarification and necessary multidisciplinary coordination.  \nCase Presentation  \nA 75-year-old retired male, living independently with his wife, was referred to Internal Medicine for evaluation of persistent abnormalities on routine blood tests identified during primary care follow-up. He reported no symptoms, including fatigue, fever, weight loss, night sweats, infections, bleeding","cbCaiv8QD6M30gWf","https://ap.wps.com/l/cbCaiv8QD6M30gWf","pdf",2374570,"English","# Abstract\n# Introduction\n# Case Presentation","[{\"question\":\"Why was the hairy cell leukemia diagnosis delayed initially?\",\"answer\":\"HCL often presents with subtle, nonspecific laboratory abnormalities. In this case, isolated thrombocytopenia and relative lymphocytosis were incidental, which can be mistaken for benign or age-related changes.\"},{\"question\":\"What tests supported the diagnosis of classical HCL in this case?\",\"answer\":\"Peripheral blood smear showed lymphoid cells with cytoplasmic projections suggestive of hairy cells. Flow cytometry then confirmed a dominant clonal population consistent with classical HCL.\"},{\"question\":\"How did the renal lesion influence clinical management?\",\"answer\":\"CT imaging found a renal lesion suspicious for carcinoma. This incidental finding led to prioritizing urological intervention and highlighted multidisciplinary coordination when concurrent malignancies are present.\"}]","Hidden in Plain Sight - Unmasking Hairy Cell Leukemia Through Structured Clinical Reasoning | PDF",1790682490,13]