Clinical context

An elderly patient with lswollen gums

At a glance

Stain	MGG

About Acute Monoblastic Leukaemia with Auer rods

This patient has Acute Monoblastic Leukaemia (AMoL). AMoL (formerly FAB AML-M5) is famous for presenting with weird extra-medullary lymphs of leukaemia (confusing called myeloid sarcomas). Monoblastic leukaemia can present with skin lumps, bleeding and enlarged gums, and the blood film that we see here. AMoL is associated with a t(9;11) chromosomal translocation and causes a gene fusion between KMT2A(MLL) and MLLT3(AF9). This type is particularly associated with gum swelling and skin infiltrates. It is difficult to treat, and is classified as intermediate risk under the WHO criteria. .

Not all the malignant cells are blasts here. When reviewing monolastic leukaemia, normally we count undifferentiated blasts, monoblasts and promonocytes under the heading 'blasts'. This is important because often traditional blasts aren't that big a feature, but the film is quite clearly abnormal.

This film is also a good example of auer rods - there are several examples (#1, #2, #3, #4, #5 and #6).

The blood film shows the other features one might associate with an acute leukaemia - a leucoerythoblastic appearance with nRBC, neutropenia and thrombocytopenia and some red call anisopoikilocytosis.

Morphological features

Auer Rod

Auer Rods

Monocytoid Blast

This cell is undoubtedly a blast - high NC ratio, open chromatin, however there are vacuolations which are coarser than lymphoid ones seen in Burkitt's type cells. This is a monoocytoid blast.

Nucleated Red Blood Cell

an nRBC is present here showing that there is an infiltrative bone marrow process.

Promonocytes

These cells are not blasts - the NC ratio and shape are wrong, although the chromatin remains somewhat open. They are clearly heading towards monocytes but are not yet mature. They are promonocytes.

Blast

An undifferentiated blast, with no monocytoid (or other) features.

Blast with Auer rod

This blast cell has a thin densely stained line within the cytoplasm. They are fused primary (azurophilic) granules from the cytoplasm of immature white blood cells. They can be found in isolation, as this one is, or there may be many of them packed into the cell.

Blast with Auer Rod

This blast has a small, azurophillic rod in the cytoplasm which is called an auer rod. Auer rods are made of fused primary granules and lysosomes that clump together. There are found only in myeloid malignancies and are characteristic of AML. Sometimes there will be one or two Auer rods in a cell, sometimes there will be many and it will be packed.

Monocytoid Blasts

These blasts are definitely monocytoid - the blue cytoplasm, vacuolation and nuclear outline are all consistent with this. In acute myeloid leukaemia with monocytoid maturation, we also count promonocytes in the blast count.

Monocytoid blast with Auer Rod

This monocytoid blast has a small auer rod near the vacuoles.

Auer Rod

This pink line is an Auer rod. It is made of fused primary granules and lysosomes that clump together. It is a finding only in acute myeloid leukaemia and they are never seen in normal healthy blood films.

Promonocyte

The line between promonocyte and blast is a fine one - they are very close in the differentiation pattern. In this case, the involutes nucleus, beginning of nuclear clumpgin and the presence of a prominent golgi zone push more towards promonocyte than blast. However, for the purposes of AML these are both counted as blasts.

See these findings at full magnification

The complete digital slide behind this page can be examined at any magnification, with all of its teaching annotations, by registered users. Registration is free for NHS and Irish haematology trainees.