全血细胞减少症是一种复杂的疾病，其特征是红细胞 (RBC)、白细胞 (WBC) 和血小板 (PLT) 水平降低。它可能是由于生产受损、外周破坏或两者兼而有之而引起的。全血细胞减少症的原因包括感染和药物反应等可逆因素以及不可逆的情况。维生素 B12 缺乏症是一种值得注意的可逆性原因，由于储存的维生素 B12 缺乏，可能需要数年时间才能在成人身上显现出来。然而，吸收受损引起的缺陷，特别是由于缺乏内在因子（IF），可能会导致两到五年内迅速恶化。一名健康的 39 岁男性，具有运动生活方式，在几天内出现头晕、恶心、呕吐、心悸和昏厥等症状。在出现这些症状之前，会出现持续数周的身体疼痛、头痛、虚弱、每日发烧、发冷和盗汗。生命体征稳定。体检发现结膜苍白，下颌下和颈部浅表区域淋巴结肿大。初始血液检查显示正细胞性贫血（Hgb 4.9、MCV 80）、白细胞减少（2.99）、血小板减少（142）和肝酶升高（AST 199、ALT 96 和总胆红素 2.04）。外周血涂片可见泪滴细胞和低色素细胞。考虑到临床表现，例如盗汗、颈部淋巴结肿大、主观日常发热以及全血细胞减少等临床表现，最初的印象是血液系统恶性肿瘤，包括但不限于白血病、淋巴瘤或骨髓纤维化。患者接受了一剂生理盐水并输注了两个单位的浓缩红细胞。胸部、腹部和骨盆 CT 扫描未发现淋巴结肿大或脾肿大。尽管最初的临床评估表明存在潜在的血液恶性肿瘤，但包括 SPEP、网织红细胞计数/分数、血清叶酸和血清维生素 B12 在内的综合检测显示，仅严重维生素 B12 缺乏，水平低于 150，且存在 IF抗体。治疗包括住院强化维生素 B12 注射，然后是详细的门诊治疗方案。患者连续 7 天完成每日剂量的维生素 B12 注射，随后在接下来的 4 周内每周注射一次。随后的实验室结果显示，WBC 计数增加至 8.39，Hgb 水平增加至 13.2，PLT 计数增加至 249，表明对维生素 B12 替代疗法有持续的积极反应。总之，全血细胞减少症提出了诊断挑战，需要仔细评估患者数据和全面测试。维生素 B12 缺乏（包括恶性贫血 (PA)）是需要考虑的可逆因素之一。在选择骨髓活检等更具侵入性的措施之前，这一点具有重要意义。营养缺乏需要首先考虑为全血细胞减少症的差异，即使没有维生素 B12 缺乏的典型症状（如大红细胞增多症和多分叶中性粒细胞），并且存在指向血液恶性肿瘤的令人信服的临床指征。版权所有 © 2024，Choi 等等人。

Pancytopenia is a complex medical condition characterized by decreased levels of red blood cells (RBCs), white blood cells (WBCs), and platelets (PLTs). It can arise from impaired production, peripheral destruction, or a combination of both. The causes of pancytopenia range from reversible factors like infections and medication reactions to irreversible conditions. Vitamin B12 deficiency is a notable reversible cause that can take years to manifest in adults due to stored reserves. However, deficiencies caused by impaired absorption, especially due to the lack of intrinsic factors (IFs), can lead to rapid deterioration within two to five years. A healthy 39-year-old male with an athletic lifestyle presented with symptoms such as dizziness, nausea, vomiting, palpitations, and fainting over a few days. These symptoms were preceded by weeks of persistent body aches, headaches, weakness, daily fevers, chills, and night sweats. Vital signs were stable. The physical examination revealed conjunctival pallor and lymphadenopathy in the submandibular and superficial cervical regions. Initial blood tests showed normocytic anemia (Hgb 4.9, MCV 80), leukopenia (2.99), thrombocytopenia (142), and elevated liver enzymes (AST 199, ALT 96, and total bilirubin of 2.04). The peripheral smear showed tear-drop cells and hypochromic cells. The initial impression was hematologic malignancy, including but not limited to leukemia, lymphoma, or myelofibrosis given clinical findings such as B-symptoms like night sweats, neck lymphadenopathy, and subjective daily fever, along with pancytopenia. The patient received a bolus of normal saline and a transfusion of two units of packed RBCs. CT scans of the chest, abdomen, and pelvis showed no adenopathy or splenomegaly. Although initial clinical assessment pointed toward a potential hematologic malignancy, comprehensive testing, including SPEP, reticulocyte count/fraction, serum folate, and serum vitamin B12, revealed only severe vitamin B12 deficiency, with a level of less than 150, with the presence of IF antibodies. Treatment involved intensive in-patient vitamin B12 injections followed by a detailed outpatient regimen. The patient completed a daily dose of vitamin B12 injections for seven consecutive days, followed by weekly injections for the next four weeks. Subsequent laboratory results demonstrated an increase in WBC count to 8.39, Hgb level to 13.2, and PLT count of 249, indicating a continued positive response to the vitamin B12 replacement therapy. In summary, pancytopenia poses a diagnostic challenge that demands careful evaluation of patient data and comprehensive testing. Vitamin B12 deficiency, which encompasses pernicious anemia (PA), is among the reversible factors to consider. This aspect holds significance before opting for more invasive measures like a bone marrow biopsy. Nutritional deficiencies need to be considered first as differentials in pancytopenia, even in the absence of typical signs of vitamin B12 deficiency (like macrocytosis and hypersegmented neutrophils) and in the presence of compelling clinical indications pointing to a hematologic malignancy.Copyright © 2024, Choi et al.