Myeloma is often described as being a very individual disease; both in terms of the way patients experience complications and in the way they respond to treatment, all of which can vary greatly. Some of this variation is due to the different types and sub-types of myeloma.
Different types and sub types of myeloma are based on the type of immunoglobulin (paraprotein) produced by the myeloma cell.
Each immunoglobulin is made up of a specific structure containing two principal components, heavy chains of which there are two, and light chains of which there are also two (see Figure 2).
Insert Fig 2
Each individual immunoglobulin (Ig for short), can have only one of the five possible heavy chain types these are denoted by the letters G,A,D,E and M and only one of the two possible light chain types. The light chain component is denoted by the Greek letters, Kappa (ƙ) and Lambda (ƛ).
Most people with myeloma, about 65%, have what is called IgG type myeloma.
That is immunoglobulin type G (one of the five possible heavy chains), with either the kappa of lambda light chain component.
The next most common type is IgA myeloma also with either kappa or lambda light chains. IgD, IgE and IgM type myeloma are all quite rare..
At the same time as producing one whole immunoglobulin structure, approximately 30% of patients will also produce light chains (such as kappa light chains) on their own which are detectable in the urine rather than in the blood. These excess ‘light chains’ are also known as ‘Bence Jones’ protein.
In about 20% of patients, the myeloma cells produce light chains only (no heavy chains at all). This is called ‘light chain’ or ‘Bence Jones’ myeloma.
More rarely, in less than 1% of cases, the myeloma cells produce very little or no immunoglobulin of any type which is known as ‘non-secretory myeloma’ making diagnosis and monitoring more difficult.
In some cases abnormal plasma cells may collect in the bone or tissue forming what’s known as a plasmacytoma. This can occur in addition to other features of myeloma or on its own which is referred to as a solitary plasmacytoma. Radiotherapy can be used to treat a plasmacytoma. Sometimes multiple plasmacytomas form without myeloma being found in the bone marrow, this manifestation is treated in the same way as myeloma.
The light chain or Bence Jones myelomas are the types most likely to cause kidney damage. If light chains deposit in the kidneys, nerves or other organs it can result in a conditions known as AL amyloidosis or light chain deposition disease.
Regular measurements of the paraprotein and light chains are taken to help confirm a diagnosis and determine the subtype of myeloma. Measurements are also taken during the course of the disease to help determine the response to any given therapy and for periodic restaging of the disease. Non-secretory myelomas are followed using radiology to measure bone disease (usually by PET scan) and by bone marrow biopsy where indicated.