Malignant histiocytosis (MH), abbreviated as malignant histiocytosis, is a systemic malignant proliferative and infiltrative disease of the mononuclear phagocyte system. The etiology of the disease has not yet been fully elucidated. In recent years, through immunological and molecular biological research, it has been confirmed that cases previously diagnosed as MH are essentially a heterogeneous group of diseases with different cellular origins, most of which are hematopoietic and lymphoid tumors related to the lymphoid lineage, such as Ki-1 (CD30)+ anaplastic large cell lymphoma. Only a few are malignant histiocytosis originating from the mononuclear phagocyte system. The disease progresses rapidly with a high mortality rate. It is not uncommon in children.

bubble_chart Clinical Manifestations

1. The onset is often acute, with persistent irregular fever accompanied by pallor, lack of strength, profuse sweating, emaciation, and progressive exhaustion.
2. Manifestations of infiltration and involvement in various tissues and organs include hematopoietic tissue infiltration leading to progressive anemia and bleeding; hepatosplenomegaly and lymphadenopathy, with jaundice often appearing in the advanced stage; skin infiltration resulting in hemorrhagic or nodular rashes; abdominal pain and abdominal masses; the respiratory, digestive, urinary, nervous, cardiovascular systems, and serous cavities can all be affected, presenting corresponding symptoms and signs.

bubble_chart Auxiliary Examination

1. Most cases present with pancytopenia in the blood picture, while a minority may show elevated white blood cell counts, but with decreased neutrophil alkaline phosphatase. Abnormal histiocytes can be found in some cases. The detection of abnormal histiocytes in concentrated venous blood (buffy coat) smears aids in diagnosis.
2. The bone marrow is usually hypercellular, displaying various atypical histiocytes. Among these, abnormal histiocytes and multinucleated giant histiocytes serve as the primary cytological basis for diagnosing MH. In contrast, lymphoid-like, monocyte-like histiocytes, and phagocytic histiocytes lack specific diagnostic significance. A single negative bone marrow examination does not rule out the disease; repeated and multi-site punctures can improve the positive detection rate.
3. Pathological examinations, including bone marrow, liver, spleen, lymph node biopsies, or lymph node puncture smears, skin lesion imprints, and pleural/ascitic fluid smears, may reveal infiltration by various abnormal histiocytes. The identification of abnormal histiocytes and multinucleated giant histiocytes holds definitive diagnostic value.
4. Histochemical and immunophenotypic analyses of MH show that abnormal histiocytes in the bone marrow and affected tissue cells exhibit histiocytic marker enzymes: cytoplasmic lysozyme positivity, nonspecific esterase positivity (inhibited by sodium fluoride), and negativity for peroxidase and myeloperoxidase (MPO). Sudan B staining is negative, and α-ASD-chloroacetate esterase is blocked. Immunohistochemical tests revealing α1-antitrypsin (AT) and α1-antichymotrypsin (ACT) positivity suggest malignant histiocytes. Immunophenotyping demonstrates monocyte-macrophage-related markers CD68+ (Kp-1+) and pan-T-cell marker Ki-1- (CD30)-. Molecular-level testing does not detect TCR or Ig gene rearrangements.

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bubble_chart Treatment Measures

1. Supportive treatment is essentially the same as for acute leukemia.
2. Chemotherapy Although chemotherapy has some efficacy, the results are unsatisfactory. In recent years, reports have indicated that regimens such as CHOP and COPP yield better outcomes. Common chemotherapy regimens include: VCP: VCR (vincristine) 2mg/m², once weekly, IV. Pred (prednisone) 40–60mg/(m²·d), orally. CTX (cyclophosphamide) 250mg/m², once weekly, IV. CHOP: CTX 750mg/m², IV, day 1. VCR 2mg/m², IV, day 1. ADM (doxorubicin) 50mg/m², IV, day 1. Pred 60mg/(m²·d), orally, days 1–5. COPP: CTX 600mg/m², IV, days 1 and 8. VCR 1.5–2mg/m², IV, days 1 and 8. PCZ (procarbazine) 100mg/m², orally, days 1–14. Pred 40mg/(m²·d), orally, days 1–14. COAP: Same as for acute leukemia. Reports suggest that the CHOP regimen can achieve a remission rate of over 50%. Adding VP-16 to the CHOP regimen, incorporating bleomycin 4mg/m² between COAP cycles, or increasing the dose of MTX therapy may enhance efficacy.

bubble_chart Differentiation

This disease needs to be differentiated from acute leukemia, variant T-cell lymphoma, Langerhans cell histiocytosis, and reactive histiocytosis. In differential diagnostic examinations, immunohistochemical analysis using various monoclonal antibodies is crucial, such as employing CD30 and CD45Ro (UCH-LI) to exclude lymphomas of T-cell origin.