**2. Data of the patients with multiple myeloma**

MM is generally a disease of older animals, although some reports exist in young animals. In dogs, the average age of diagnosis is between 8 and 12 year-old [9-10,15,19-25].There is a report of MM in a younger dog, 4-year-old [26]. There is no apparent gender predisposition

© 2013 Muñoz et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

in dogs. Further, the largest retrospective study to date (60 dogs) included 30 males and 30 females [27].

**4. Clinical signs**

pneumonia [1,3,37,60].

**4.2. Bone pain and skeletal lesions**

**4.1. Increased susceptibility to infections**

The infiltration of various organ systems by neoplastic cells, the production of cytokines by the tumor or the bone marrow microenvironment, and the high circulating level of a single type of immunoglobulin lead to a wide array of clinical manifestations. Therefore, the clini‐ cal signs of MM vary with the level of plasma cell proliferation, the location and spread of the neoplastic plasma cells, and the nature and extent of the proteinuria [3,4,9-10,15,33,54]. The clinical signs are generally non-specific and include lethargy, renal failure, hemostatic abnormalities, anorexia, diarrhea and vomiting in small animals and weight loss, anorexia,

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MM patients are usually immunocompromised and thus highly susceptible to infections [55]. MM associated immunodeficiency is likely a multifaceted phenomenon secondary to decreased concentration of polyclonal immunoglobulin [56], suppression of macrophage-re‐ lated factors influencing the normal B cell differentiation to plasma cells [57] in response to antigenic stimulation [58], decreased T helper cell function, increased rate of γ-globulin ca‐ tabolism, neoplastic infiltration of bone marrow resulting in leukopenia [59], dysfunctional

In cats with MM, the most common infectious processes include periodontitis, chronic re‐ current upper respiratory infections and terminal bacteriemia [4]. In horses with MM, the most common system affected by infectious disease is the lung, with several cases of severe

Bone pain is considered one of the most common presenting complaints in human patients [61-62]. Skeletal abnormalities are commonly recognized in small animals, but uncommon in horses with MM [1,3,63]. Horses frequently had bone lesions, therefore, bone pain might

The percentage of cats with MM and radiographically-evident skeletal lesions was 58.3% [2,4,13,63-66], similar to the 50-60% occurrence reported for dogs [27,64]. Skeletal lesions can be either solitary (well-circumscribed with areas of osteolysis or punched-out lytic areas) or multiple (generalized osteopenias) [4,27]. Rarely, pathologic fractures are seen. Skeletal le‐ sions are typically identified in bones involved in active hematopoiesis (e.g. ribs, vertebrae, pelvis, and proximal and distal aspects of long bones). Other causes of focal osteolysis are rare in companion animals, but include carcinomas [67], giant cell tumors of bone [68], be‐ nign aneurismal bone cysts [69-71] and bone lesions secondary to tumor invasion [70,72-73]. Generalized osteopenias have also been diagnosed radiographically [4]. Demineralization of bone in humans is detected through measurement of bone mineral density, a technique not used routinely in veterinary medicine. Generalized osteopenias is not specific for MM, and

manifest more as a gait abnormality and therefore, it could be misdiagnosed.

may also be seen with nutritional, renal and metabolic disorders [74-77].

and/or decreased numbers of neutrophils, and defective complement activation [3-4].

fever, increased susceptibility to infections and limb edema in horses [1,3,8,11,36].

The mean age of diagnosis in cats ranges between 12.5 and 14 years, and most of the cats with MM are older than 7 year-old [28,29,4,30,31,32,33,9]. According to the literature, the youngest cat with MM was 1.5 year-old [31]. A myeloma-related disorder has been described for a 19-month-old cat [34]. Males accounted for about 55-56%. The age and gender in dogs and cats with MM are similar to those described in human patients. In a large retrospective study of 1027 people, the average age of diagnosis was 66 years and 59% were men [35].

MM is also a neoplasm of elderly horses, with mean age of 11 years at the moment of the diagnosis [1]. Horses with this condition have ranged in age from three months to 25 years. The youngest animals were a 1.6-year-old Quarter Horse mare [36] and a 3 month-old Quar‐ ter Horse colt [37]. Although it was suggested initially that it could be more common in Quarter Horses [1], there are too few reports in equids for statistical interpretation of this data. Both male (geldings and stallions) and female horses are represented equally.
