Introduction: Mantle cell lymphoma (MCL) is an aggressive B-cell non-Hodgkin lymphoma. Patients often present with lymphadenopathy, early satiety, and B-symptoms. Despite up to 92% of MCL patients having peripheral blood involvement by flow cytometry, presentation with leukemic involvement and hyperleukocytosis are uncommon. Hyperleukocytosis, marked by a white blood count (WBC) >100 x 10 9/L, often leads to symptomatic leukostasis due to tissue hypoxia, generally found in acute leukemias. We conducted a systematic review of leukostasis in MCL, and present a case we encountered in our clinical practice of a non-nodal MCL variant showing leukostasis, spontaneous tumour lysis syndrome (TLS), and severe anemia to identify treatment strategies and outcomes. Methods: We searched PubMed for peer-reviewed articles and abstracts on “mantle cell lymphoma,” “hyperleukocytosis,” and “leukostasis.” All articles and abstracts that discuss hyperleukocytosis leading to leukostasis in MCL were included. Results: The search yielded eight results. After exclusions, five case reports and abstracts were included. These studies featured different MCL variants, presenting WBCs ranging from 121 to 1227 x 10 9/L, and various leukostasis symptoms. Leukapheresis was used in all five published cases, leading to lower WBCs and symptom improvement. Results are summarized in Table 1. Our patient was found to have the small lymphocyte variant of MCL, with WBC of 543.3 x 10 9/L on presentation. Our facility does not have leukapheresis capability. As a result, our initial treatment consisted of only supportive care and escalating doses of corticosteroids, with close monitoring for TLS. To our knowledge, this report is the first demonstration that IV methylprednisolone, without leukapheresis, is effective for acute management of leukostasis. Our patient's WBC reduced from 543.3 x 10 9/L to 230 x 10 9/L, leading to improved neurological function and oxygenation. Steroids were particularly useful in our patient with secondary, MCL-related warm autoimmune hemolytic anemia. Conclusion: This review highlights the importance of recognizing non-specific leukostasis symptoms, even in patients with mature B-cell lymphoproliferative disorders. Leukapheresis is effective in treating leukostasis in MCL patients. In hospitals without leukapheresis, escalating doses of IV methylprednisolone can be considered as a safe and effective strategy.