Page 179 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Disorders of Calcium: Hypercalcemia and Hypocalcemia 169

Alkali Administration dogs, 426,453 although it may be more common than
The administration of alkaline agents may result in the previously reported because the Ohio State University
oncology service has documented seven cases (Couto,
development of hypocalcemia. Symptomatic hypocalce-
personal communication, 2004).
mia was documented in a cat treated for salicylate intoxi-
2
cation with sodium bicarbonate. Muscle fasciculation
increased during treatment with sodium bicarbonate, Nutritional Secondary
and serum tCa was low. A single dose of intravenous Hyperparathyroidism
sodium bicarbonate at 4 mEq/L to cats resulted in a max- Vitamin D deficiency and nutritional secondary hyper-
imal decrease of iCa 10 minutes following infusion; iCa parathyroidism associated with low calcium and/or high
remained below baseline for 3 hours. 114 Part of the phosphorus concentrations in the diet result in low serum
decrease in iCa was attributed to dilution and part to iCa and phosphorus concentrations, with an increase in
increased pH of serum, but most of the decrease was PTH secretion. Nutritional secondary hyperparathyroid-
the result of unidentified factors. Similar findings were ism may also occur when severe gastrointestinal disease is
noted in dogs receiving sodium bicarbonate infusion. 380 present, limiting the absorption of calcium and vitamin
Twitching has been observed on rare occasion during or D. Increased PTH secretion tends to return serum iCa
shortly after infusion of sodium bicarbonate solutions in concentration to normal, but decreases serum phospho-
cats with urethral obstruction and in dogs or cats with rus concentration. 623 The occurrence of nutritional sec-
renal failure (Chew, personal observations) presumably ondary hyperparathyroidism has decreased dramatically
because of decreases in serum iCa. since the advent of feeding commercially available, nutri-
tionally complete and balanced pet food. 286 Nutritional
Acute Reversal of Chronic Hypercalcemia
secondary hyperparathyroidism was induced in adult
The sudden correction of chronic hypercalcemia can beagles by feeding a diet high in phosphorus and low
result in hypocalcemia as a result of parathyroid gland in calcium, with a calcium to phosphorus ratio of
atrophy and inadequate ability to synthesize and secrete 1:10. 128 A significant increase in PTH production was
PTH. This happens frequently in dogs with primary seen at 10 weeks of feeding, and cancellous bone volume
hyperparathyroidism caused by parathyroid gland ade- was reduced by 20% to 30%. Under experimental
noma following surgical excision of the affected parathy- conditions, puppies fed a low-calcium, normal phospho-
roid gland(s). The degree of parathyroid gland atrophy rus content diet exhibited increased concentrations of
depends on the magnitude of hypercalcemia and its dura- PTH and calcitriol, with a decrease in 24,25-dihydrox-
tion before correction. Two dogs with spontaneous yvitamin D concentration. 239 In five German shepherd
infarction of a parathyroid gland adenoma have been dog puppies fed a diet consisting of 80% steamed rice
reported with the development of hypocalcemia and clin- and 20% raw meat, nutritional secondary hyperparathy-
ical signs. 485 Rapid correction of hypercalcemia following roidism was observed. 289 This diet apparently had an
chemotherapy for lymphosarcoma or surgical excision of adequate calcium concentration but contained an excess
anal sac adenocarcinoma often results in mild hypocalce- of phosphorus. All puppies showed moderate to marked
mia that is usually not associated with clinical signs, but fibrous osteodystrophy.
clinical signs of hypocalcemia may occur. 259 Persistent Serum iCa and phosphorus concentrations were below
hypocalcemia has been observed in dogs following para- the reference range in six young cats with nutritional sec-
thyroidectomy in association with hypomagnesemia. In ondary hyperparathyroidism. 573 Clinical signs referable
three dogs, hypocalcemia resolved following supplemen- to hypocalcemia (excitation, muscle twitching, seizures)
tation with magnesium salts, but calcium regulatory and spontaneous fractures of bones were present in most
hormones were not measured (Chew, unpublished cats. Renal secondary hyperparathyroidism preferentially
observations). affects the bones of the face (fibrous osteodystrophy),
whereas nutritional secondary hyperparathyroidism tends
Tumor Lysis Syndrome to cause osteopenia of the long bones and vertebrae.
Tumor lysis syndrome occurs when there is rapid destruc- Calcitriol concentration was mildly increased in three of
tion of sensitive tumor cells (usually lymphoid or bone four cats in which it was measured, whereas 25-
marrow tumors) following chemotherapy. 440 Release of hydroxyvitamin D was mildly decreased in three of three
intracellular products can result in hyperkalemia, cats. PTH concentrations were increased in all cats and
hyperphosphatemia, and hyperuricemia. Hypocalcemia ranged from a minimal increase in one cat to a marked
can develop as calcium-phosphate salts are deposited into increase of 4 to 9.7 times the upper range in the
soft tissues by mass-law effects from markedly increased remaining five cats. Cats had been fed meat only (three
serum phosphorus 95,426,453 and may be associated with cats), meat combined with vegetables (two cats), or
the development of AIRF. Tumor lysis syndrome is a vegetables only (one cat). Dietary calcium intake was less
rarely reported cause of symptomatic hypocalcemia in than one tenth of the minimal nutritional requirement;