AMoL (M5)

Acute Monocytic Leukemia

• The FAB classification system divides acute monocytic leukemia into two subtypes: (M5a) poorly differentiated, and (M5b) well differentiated.
  
  
• M5a is characterized by a predominance of monoblasts, which typically are large, with abundant cytoplasm, and distinct nucleoli.
  
  
• M5b is characterized by a spectrum of monocytic differentiation including promonocytes and monocytes. The peripheral blood usually contains more monocytes than the bond marrow, in which the predominant cell is the promonocyte. This cell has abundant cytoplasm, its nucleus shows delicate folding or lobulation, and nucleoli may be seen. Extramedullary tissue infiltration accounts for skin and gingival involvement.
  
  
• Both subtypes of M5 show greater than 80 % positivity with the NSE stain.
  
  
• Peroxidase and Sudan Black B stains are negative or only weakly positive.
  
  
• Lymphadenopathy frequently occurs, and sometimes the spleen and liver are markedly enlarged. Central nervous system involvement also has an increased incidence in these patients.
  
  
• WBCs are frequently elevated, increased lysozyme levels, renal failure, and hypokalemia. DIC is relatively common, although hemorrhagic features are not as prominent as in patients with acute promyelocytic leukemia.
  
  
• Muramidase (serum and urine lysozyme levels) are often elevated in cases of AML that have a significant monocytic component, including both M4 and M5.
  
  
• Lysozyme is a hydrolytic enzyme found in mature monocytes and to a lesser extent, in granulocytes. Serum and urine levels of this enzyme are elevated when there is rapid cell turnover. Such elevations are most striking in the monocytic leukemias and are directly proportional to the amount of monocytic differentiation. They are more elevated in cases of M5b than in M5a. Those patients who have heavy urinary excretion of lysozyme may develop a renal tubular defect that results in hypokalemia, hypocalcemia, and azotemia.
  
  

PROGNOSIS

Poor - 5 months