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492 Hypercalcemia, Idiopathic Feline

○ Assess calcium × phosphorous (Ca • PO 4 ) ○ Parathyroid glands should be ≈1.3-3.3 mm • Plicamycin
in greatest width (dogs and cats).
product: if > 60, nephron damage is a ○ In dogs with PHPTH, a mass is typically • Cinacalcet
VetBooks.ir • Urinalysis identified involving one or more parathy- Chronic Treatment
concern. In PHPTH, typically < 45.
roid gland(s), usually 4-8 mm in greatest
○ Uroliths and calcium-containing crystal-
Treat inciting cause
luria are common.
diameter.
○ All causes of hypercalcemia lead to poorly ○ Dogs with renal secondary hyperparathy- Possible Complications
concentrated urine (by nephrogenic roidism have enlargement of two, three, Overcorrection (hypocalcemia), urolithiasis,
diabetes insipidus). or all four parathyroid glands. nephron damage (if Ca • PO 4 > 60)
○ Persistent isosthenuria (1.008-1.012) • Additional testing based on abnormalities
with concurrent azotemia suggests kidney identified (e.g., fine-needle aspiration of Recommended Monitoring
disease or hypoadrenocorticism. enlarged lymph nodes, fungal serology) • Serum total and ionized calcium
○ Hyposthenuria, isosthenuria, or minimally concentrations
concentrated urine associated with PHPTH TREATMENT • Renal parameters
(mean ≈1.011), with values as low as 1.002. • Serum electrolytes
• Thoracic radiographs Treatment Overview
○ Nodular lung patterns or lymphadeno- Successful treatment of underlying cause lowers PROGNOSIS & OUTCOME
megaly suggest neoplasia or fungal disease. serum calcium. If (Ca • PO 4 ) is > 60, additional
○ Cranial mediastinal mass common in measures may be required. Rapid reduction in • Varies; depends on ability to achieve nor-
dogs that have hypercalcemia secondary serum calcium, even with extremely increased mocalcemia and correct underlying cause
to lymphoma. values (15-23 mg/dL) is not necessary if (Ca • • Excellent for PHPTH
○ Lytic bone lesion suggests multiple PO 4 ) is < 60, which is typical of PHPTH. Even
myeloma or other metastatic cancer. when calcium is within reference range, if Ca • PEARLS & CONSIDERATIONS
• Abdominal imaging (ultrasound ± radiographs) PO 4 is increased, nephron damage may ensue.
○ Lesions suggesting malignancy (lymph- Comments
adenopathy, hepatosplenomegaly, possible Acute General Treatment • Remember, renal failure is not caused by
metastases, including lytic bone lesions) Primary (most efficacious): hypercalcemia alone.
○ Uroliths (calcium phosphate, calcium • IV fluid therapy (calcium free; avoid lactated • Correcting total calcium concentration for
oxalate, or both) and bladder wall thicken- Ringer’s solution) hypoalbuminemia or hyperalbuminemia is
ing: common in PHPTH ○ Dilution of serum calcium and phosphorus not reliable (instead, measure serum ionized
○ Assess renal structure. Renal dystrophic concentrations, improved glomerular calcium concentrations directly).
mineralization rarely is apparent radio- filtration rate • Oral consumption of calcium alone does
graphically or ultrasonographically. ○ Twice maintenance plus dehydration not cause hypercalcemia.
deficit should be administered over the • Hypercalcemic dogs that are ill are not likely
Advanced or Confirmatory Testing first 24 hours, assuming no heart disease, to have PHPTH.
• Ionized calcium (i.e., biologically active oliguria, or other factor predisposing to
component of the total serum calcium): intolerance of volume load; adjust accord- Technician Tips
normal or low with CKD, increased with ing to clinical signs. • Urolithiasis related to hypercalcemia can
most other causes of hypercalcemia (e.g., • Furosemide 2-3 mg/kg IV q 4-8h. Calciuric cause urinary obstruction. Straining to
PHPTH, hypercalcemia of malignancy, diuretic (unlike thiazide diuretics or spirono- urinate is an emergent condition.
vitamin D toxicosis) lactone) is not recommended for pets with • Hypercalcemic dogs should always have
• Serum PTH and PTHrP concentrations renal insufficiency. drinking water available and should be given
during hypercalcemia • Glucocorticoids (prednisone or dexametha- ample opportunity to urinate.
○ PTH should be undetectable in response sone): decrease intestinal calcium absorption,
to hypercalcemia. increase renal calcium excretion. Diagnostic SUGGESTED READING
○ PTH values within or above reference samples (e.g., lymph node aspirate, bone Skelly BJ: Primary hyperparathyroidism. In Ettinger
range are consistent with PHPTH. marrow aspirate, liver biopsy) should be SE, et al, editors: The textbook of veterinary
○ Undetectable PTH and detectable PTHrP obtained before treatment because steroids internal medicine, ed 8, St. Louis, 2017, Elsevier,
concentrations are consistent with hyper- may mask lymphoma. pp 1715-1727.
calcemia of malignancy. Secondary therapies (more expensive and not AUTHOR: Edward C. Feldman, DVM, DACVIM
• Serum vitamin D concentrations: if suspect often required): EDITOR: Leah A. Cohn, DVM, PhD, DACVIM
intoxication (p. 164) • Bisphosphonates
• Cervical ultrasound • Calcitonin

Hypercalcemia, Idiopathic Feline

Epidemiology RISK FACTORS
BASIC INFORMATION
SPECIES, AGE, SEX Genetics, diet, or the use of urinary acidifiers
Definition Cats of any age (often 5-10 years) and either sex
This poorly understood condition is the most ASSOCIATED DISORDERS
common cause of increased ionized calcium GENETICS, BREED PREDISPOSITION Calcium oxalate urolithiasis, chronic kidney
(iCa) in cats. Long-haired cats appear to be overrepresented. disease (CKD)

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