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Diagnosis of myeloma and plasmacytoma

Lateral skull X-ray showing multiple lytic deposits.
Lateral skull X-ray showing multiple lytic deposits.

The basic peripheral blood count usually demonstrates an anaemia and the erythrocyte sedimentation rate (ESR, a basic test of active disease ongoing in the body) is usually very elevated due to the coating of the erythrocytes (red cells) with immunoglobulin. 

 

An immunoglobulin electrophoresis performed on the blood serum gives a characteristic picture in most cases. There is a very high spike on the electrophoretic strip indicating an over-expression in the serum of one protein type, (which is, of course, the immunoglobulin that the malignant clone of cells makes) and is often a suppression (immune paresis) of the other immunoglobulins.

 

The abnormal immunoglobulin is referred to as the abnormal paraprotein and the level of this paraprotein can and will be quantified by the doctor; serial measurements of this level assist the monitoring of the disease.

 

The immunoglobulin molecules are made up of two component heavy chains of peptides and two light chains; in myeloma, there is an overproduction and mismatch of light chain and heavy chain synthesis and an excess of the light chains, which are of sufficiently low molecular weight that they pass through the kidneys unimpeded and appear in the urine. They are detectable in the urine by a relatively simple test, and this test for such proteins is called the Bence-Jones protein test after the man who observed it first; a positive test is almost pathognomonic/diagnostic for myeloma. Nowadays, it is routine that the levels of free light chains in the serum can also be measured and the serial assessment of these levels of the abnormal paraprotein or free light chains help the doctor in the serial assessment of the disease process once the diagnosis has been made.

 

A skeletal survey refers to the x-raying of the entire skeleton to look for bony lesions and is performed in the work up of all myeloma cases; interestingly, isotope bone scans under-read the situation in myeloma and are considered inferior diagnostic tests to plain x-rays. In a typical case, there are multiple lytic (i.e. black on x-ray) lesions in multiple bones.

 

 For example, the skull is very typically involved and where this is heavily diseased, it has multiple holes in it on lateral skull x-ray and the term ‘pepper pot skull’ is used in the medical profession, as the skull appears with the rounded holes, such as is seen in the top of a pepper pot - the photo shows a typical 'pepper-pot' skull - a side x-ray view of a myeloma patient's skull showing the many 'punched-out' lytic skull lesions of myeloma). These are truly multiple plasmacytomata.

 

The last and most important test is the bone marrow examination, the discovery of abnormal/malignant plasma cells in the bone marrow proves for sure that the diagnosis is that of multiple myeloma (the photo in the 'Incidence' sub-section of this myeloma section shows a typical example of the marrow appearances of myeloma in the bone marrow).

 

It should be noted that routine scanning of internal organs such as abdominal contents is not routinely helpful in this disease, because myeloma rarely affects organs outside the bones although soft tissue plasmacytoma (particularly in the head and neck region) are well recognised.

 

To establish the diagnosis of plasmacytoma, the doctor has to prove that there is plasmacytoma on biopsy of a lesion. 

 

To prove the diagnosis of myeloma, there has to be bone disease, the bone marrow biopsy must contain at least 30% of malignant plasma cells and there is the monoclonal spike of the paraprotein on protein electrophoresis of the serum (indicating the overproduction of clonally derived immunoglobulin) or free light chains (see above).


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