Page 157 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Disorders of Calcium: Hypercalcemia and Hypocalcemia 147

the kidneys cells by binding to and activating the cell significantly more likely to have early relapse and death
membrane PTH-PTHrP receptors. This binding results compared with those with B-cell lymphoma. Shorter
in stimulation of osteoclastic bone resorption, increased remissions and survival times have been noted by others
renal tubular calcium reabsorption, and decreased renal for T-cell lymphoma compared with B-cell lymphoma in
tubular phosphate reabsorption. IL-1 stimulates bone dogs. 225 In another study, 46 (32.8%) of 140 lymphomas
resorption in vivo and in vitro and is synergistic with were classified as T cell in origin, and 16 of these dogs
PTHrP. 364,480 TGF-a and -ß can stimulate bone resorp- (35%) were hypercalcemic. 196 In 37 dogs with lymphoma
tion in vitro and have been identified in tumors associated and hypercalcemia, calcium concentration was not related
with HHM, including adenocarcinomas derived from to prognosis; mean remission was 10.4 months, and
apocrine glands of the anal sac in dogs. 374 median remission was 6 months. 477 The presence of a
mediastinal mass had an adverse effect on remission in
Lymphoma these hypercalcemic dogs. Serum tCa concentration
Hypercalcemia is found in 20% to 40% of dogs with lym- may return to normal despite minimal reduction in tumor
phoma (Fig. 6-16). 321,342 Most dogs with lymphoma and mass following chemotherapy, as happened in 5 of 12
hypercalcemia have HHM because increased osteoclastic dogs with lymphoma and initial hypercalcemia. 610 The
resorption is present in bones without evidence of tumor finding of hypercalcemia in dogs with lymphoma was
metastasis. Lymphoma is an uncommon cause of mild not prognostic for survival or time to remission, but
HHM in ferrets. 290 Lymphomas associated with HHM T-cell origin lymphoma did adversely affect
are usually of the T-cell type. 607 T-cell lymphoma prognosis. 298,561,590
occurred in 22% of dogs with lymphoma, and hypercalce- Most dogs with lymphoma and HHM have increased
þ
mia only occurred in dogs with CD4 lymphoma in one circulating PTHrP concentrations, but concentrations
study. 502 The pathogenesis of hypercalcemia in dogs with are lower than those in dogs with carcinomas and
lymphoma and HHM resembles that occurring in HHM, and PTHrP concentrations are not correlated
humans with lymphoma or leukemia induced by human with serum calcium concentration (Fig. 6-17). 489 Ele-
T-cell lymphotropic virus type I (HTLV-I). Neoplastic vated PTHrP concentrations were found in 12 of 14 dogs
cells from humans with HTLV-I-induced lymphoma with underlying malignancy, but was within the reference
have increased PTHrP production. 471 range in 17 normocalcemic dogs with lymphoma. 369 Epi-
Most dogs with lymphoma and hypercalcemia have T- thelial T-cell cutaneous lymphoma (mycosis fungoides)
cell lymphoma. 561,607 Dogs with T-cell lymphoma were has been associated with hypercalcemia in one dog, but

A B
Figure 6-16 Lateral (A) and ventrodorsal (B) thoracic radiographs of a 5-year-old boxer dog with
hypercalcemia of malignancy caused by mediastinal lymphoma (arrows). Severe hypercalcemia (serum total
calcium concentration, 20.6 mg/dL) was detected on initial presentation. (From Chew DJ, Carothers M.
Hypercalcemia. Vet Clin North Am Small Anim Pract 1989;19:265–287.)