We are pleased to receive the letter from the reader about our article. Herein, we are willing to respond to some of their comments.
In our case, we reported a senile Chinese man with a 2-month history of fever accompanied by hearing loss, myalgia, elevated serum globulin, and erythrocyte sedimentation rate. Besides a screening for autoimmune background, we naturally performed bone marrow examination to rule out hematologic disorders, which incidentally revealed low-percentage of monoclonal B-lymphocytes.
As the reader said, monoclonal B-cell lymphocytosis (MBL) is usually classified into three groups according to its immunophenotype. The majority of MBLs take the immunophenotype of typical chronic lymphocytic leukemia (CLL) as CD19(+), CD5(+), CD23(+), and FMC7(−). A minor group of MBL cases are classified as atypical CD5(+) MBL whose immunophenotype resembles mantle cell lymphoma (CD19[+], CD5[+], CD23[−], and FMC7[+]). The third group of MBL is CD5(−) which has a similar immunophenotype with splenic marginal zone lymphoma. As for the patient described in our case, flow cytometry (FCM) showed CD5(−), CD10(−), CD19(+), and FMC7(+), which should be assigned into the CD5(−) MBL with an origin from the marginal zone lymphoid tissue. As for the diagnosis of MBL, works should be done to exclude lymphoma because monoclonality detected by FCM can mean either MBL or any other CD5(−) lymphoma. Furthermore, a definite diagnosis of lymphoma should rely on the pathologic study of biopsied tissue. Ideally, the enlarged superficial lymph node should be removed for biopsy. Unfortunately, no superficial lymph node could be detected in our patient, positron emission tomography-computed tomography (PET-CT) was performed with no signs of malignancy detected. Thus, a diagnosis of MBL was established. Hence, we did not arrange FCM of peripheral blood for this patient as we believe it only leads to the same conclusion.
The updated WHO emphasizes that “low count” MBL, defined as a peripheral blood monoclonal lymphocyte count of less than 0.5 × 109/L, must be distinguished from “high count” MBL which has a higher risk of transformation into CLL or other lymphoid malignancies. Although low-count MBL has an exceedingly small risk of progression, it is hard to say whether MBL in patients with autoimmune disorder background is suggestive of benign process or not. In other words, we suspect that the transformation risk in this condition might be higher than that in healthy people due to the double effects by autoimmunity and monoclonal lymphoproliferaion. Therefore, we believe that it is necessary to perform repetitive FCM analysis and/or PET-CT evaluation in the follow-up. However, we agree that the best means and interval of follow-up for monoclonity are yet to be decided.
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2. Swerdlow SH, Campo E, Pileri SA, Harris NL, Stein H, Siebert R, et al The 2016 revision of the World Health Organization classification of lymphoid neoplasms Blood. 2016;127:2391–405 doi: 10.1182/blood-2016-01-643569