ACUTE MONOCYTIC LEUKEMIA

Acute monocytic leukemia

Acute monocytic leukemia

Description of Condition

AML-M5 is defined by more than 20% (WHO classification) or more than 30% (French American-British (FAB) classification) of myeloblasts in the bone marrow aspirate. Bone marrow monocytic cells comprise more than 80% of non-erytroid cells. In AML-M5a, more than 80% of monocytic cells are monoblasts, whereas in AML-M5b, less than 80% of monocytic cells are monoblasts; other cells show (pro)monocytic differentiation.

Clinical signs and symptoms

Children with AML in general may present with a broad variety of (atypical) symptoms, which may range from minor symptoms to life-threatening conditions. Most patients will present with fatigue and/or asthenia, which is often accompanied by (persistent) fever. Severe infections may occur due to the diminished neutrophil count and function. Easy bruising (petechiae and/or purpura) may occur as well as enhanced bleeding (epistaxis, oral or gingival bleeding, rectal blood loss, menorrhagia, cerebral hemorrhage). These bleeding disorders result from thrombocytopenia that may be associated to Disseminated Intravascular Coagulopathy (DIC), which can lead to life-threatening situations. The complications due to bleeding contribute for 7-10% to the mortality that is observed during the first days/weeks after diagnosis (Creutzig, 1987). Complications due to hemorrhage are more frequent in AML-M5. Pallor may be predominant, and results from the decreased hemoglobin level. Pallor may be accompanied by dizziness, headache, tinnitus, collaps, dyspnea and/or congestive heart failure. Cutaneous leukemic infiltration may arise in AML-M5. Gingival hyperplasia may be present, but is not typical of AML-M5.

Dyspnea and/or hypoxia may also result from leukostasis, which results in a decreased blood flow in some organs (lungs, CNS, liver, skin) due to a dramatically increased White Blood Cell count (WBC) (>100.000/ml) leading to hyperviscosity.

Neurological symptoms may occur: headache, nausea, vomiting, photophobia, cranial nerve palsies, papil edema and/or nuchal rigidity. These symptoms may result from leukostasis, but may also reveal meningeal invasion by monoblasts or be the presenting symptoms of a "chloroma", which is a soft tissue mass consisting of monoblasts. These chloromas often have an orbital or periorbital localisation, or may arise around the spinal cord, causing paraparesis or "cauda equina" syndrome. CNS leukemic infiltration occurs in 6-16% of AML (Bisschop 2001, Abbott 2003) and is frequent in AML-M5.

Renal insufficiency occurs seldomly. It is caused by hyperuricuria and/or hyperphosphaturia, leading to obstructing tubular deposits and oliguria/anuria. The etiology of these metabolic disorders is called the "tumour lysis syndrome", where monoblasts lyse spontaneously. This situation is an emergency since life-threatening hyperkalemia may be associated, requiring hemodialysis or peritoneal dialysis.

Diagnostic methods

Routine blood analysis shows in the majority of patients a normocytic, normochromic anemia, which may be as low as 3 gr/dl. Reticulocyte count is low. Erythrocyte sedimentation rate (ESR) is often increased. Thrombocyte count is mostly decreased «100.000/ml). WBC count may be decreased, normal or (substantially) increased. WBC differential (the percentage of each of the five types of white blood cells) may show myeloblasts that may contain Auer rods, which are needle-shaped accumulations of myeloid granules. However, myeloblasts are not always observed in the differential, and only promyelocytes ...