Symptoms can vary tremendously within the same patient over time, as well as between patients. Clinical signs are dependent upon the location(s) the myeloma cell is proliferating in, as well as signs attributable to the excess production of antibodies by these cancerous myeloma cells. Furthermore these tumours show differing patterns of clinical signs between different animal species.

Cats with myeloma commonly have anaemia and this can contribute to the lethargy and weakness that may be seen. The cancerous myeloma cells typically produce immunoglobulins (monoclonal antibodies), often referred to as a paraprotein or M-protein. Filtration of the paraprotein by the kidneys, leads to abnormal kidney function and even renal failure. Excessive levels of paraprotein increase the "thickness" of the blood resulting in hyperviscosity syndromes that may damage the eye (causing blindness), or the nervous system (causing nerve or brain signs) or the heart (cardiomyopathy) or blood clotting (and so bleeding tendencies). The myeloma cells can congregate in clumps in various internal organs (e.g. the liver or spleen) or within skin, causing isolated tumors (or plasmacytomas), that can interfere with the normal function of that area. If the myeloma cells proliferate in the marrow (as happens in some cats, but is more common in human patients or dogs) then destruction of bone can be seen (also known as osteolysis) causing bone pain or even fractures. Myeloma cells can also disturb the control of key body chemicals (such as calcium metabolism). Patients with myeloma can also be immunosuppressed and have a reduced ability to fight infections.

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Video clip of a 4 year old female neutered domestic short-haired cat with ataxia and a resting head tremor, secondary to hyperviscosity syndrome attributable to a myeloma related disorder with a hepatic focus.

	Subcutaneous plasmacytoma affecting the palmar aspect of a forelimb paw in a cat.
	Retinal vessel tortuosity in a paraproteinaemic cat (courtesy of Dr. David Williams, University of Cambridge).