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Hypercalcemia, Idiopathic Feline 493

Clinical Presentation • Total thyroxine (T 4 ): unremarkable • Alendronate may cause esophageal stricture
HISTORY, CHIEF COMPLAINT • Thoracic and abdominal imaging: rule out • In humans, alendronate may cause osteone-
or irritation of mucous membranes.
VetBooks.ir screening) or associated with vague clinical Advanced or Confirmatory Testing crosis of the mandible and maxilla; if dental Diseases and Disorders
neoplasia
• Usually an incidental finding (e.g., geriatric
work is required, it should be completed
signs such as weight loss, diarrhea, constipa-
tion, vomiting, or anorexia
roid hormone–related protein (PTHrP), vitamin
• The modest degree of hypercalcemia typical Serum parathyroid hormone (PTH), parathy- before starting alendronate.
of the disorder is seldom associated with D profile: Recommended Monitoring
the most worrisome adverse effects of • PTH: below or near the lower end of the Recheck iCa 6 weeks after starting diet trial or
hypercalcemia (e.g., tissue mineralization). reference range 1-2 weeks after any change in medical therapy.
• Sometimes, signs related to calcium oxalate • PTHrP: typically below limits of detection Once controlled, iCa should be rechecked q
urolithiasis (e.g., dysuria, periuria [p. 1014]) • Vitamin D: 25(OH)D 3 and 1,25(OH) 2 D 3 4-6 months. Serum chemistry profile (azotemia)
or concurrent CKD (e.g., polyuria/ polydip- within reference range and urinalysis (crystalluria) should be checked
sia [pp. 167 and 169]) are noted. q 6-12 months.
TREATMENT
PHYSICAL EXAM FINDINGS PROGNOSIS & OUTCOME
No specific physical exam findings. Calcium Treatment Overview
oxalate urolithiasis can cause signs of urethral Because the degree of hypercalcemia is typically With treatment, excellent. Without treatment,
obstruction in some affected cats. modest, emergent efforts to reduce calcium are urolithiasis remains a concern.
not required. After other causes of hypercalcemia
Etiology and Pathophysiology have been ruled out, dietary therapy is typically PEARLS & CONSIDERATIONS
• Extracellular total calcium fractions include begun. If unsuccessful, medical management
biologically active iCa (≈52%), protein- is attempted. Concurrent urolithiasis and/or Comments
bound calcium (≈40%), and calcium com- CKD must be addressed, if present. • Other causes of hypercalcemia may be associ-
plexed to other molecules (≈8%). Calcium ated with life-threatening disease and should
balance is closely controlled in health through Acute General Treatment be ruled out before instituting treatment for
intestinal absorption, renal excretion, and Rarely, calcium oxalate urolithiasis results in idiopathic hypercalcemia.
redistribution from bone. urethral obstruction, requiring emergency • Severe hypercalcemia is seldom caused by
• As the name implies, the cause of ionized intervention (p. 1009) idiopathic hypercalcemia.
hypercalcemia in affected cats remains • Renal damage associated with hypercalcemia
unknown. Chronic Treatment is related to the calcium × phosphorus
• Many cats can be managed with dietary product more than to the iCa. Because
DIAGNOSIS therapy alone. hypercalcemia is mild and phosphorus is
• If ionized hypercalcemia persists after a within reference range, kidney damage is
Diagnostic Overview 6-week diet trial, medical therapy with unlikely with idiopathic hypercalcemia alone.
Typically, total calcium is measured first, glucocorticoids or bisphosphonate drugs is • It is possible for a cat to have both CKD and
and if above the upper end of the reference recommended. idiopathic hypercalcemia, which can confuse
range, iCa is measured. If that too is above the ○ Prednisolone (not prednisone) 0.5-1 mg/ the diagnosis (e.g., CKD can cause increased
reference range, attempts should be made to kg PO q 12-24h. Avoid use until diag- total calcium but normal iCa).
identify a cause of hypercalcemia. Idiopathic nostic testing is complete. • Use of formulas to adjust calcium concentra-
hypercalcemia is a diagnosis of exclusion. ○ Alendronate 5-20 mg/CAT PO q 7 days. tion based on albumin is not appropriate
Begin with lower dose, and titrate up as for cats with hypercalcemia. Instead, ionized
Differential Diagnosis needed. Administer after a 12-hour fast. calcium concentrations should be measured
Hypercalcemia (pp. 491 and 1232) Pills should not be cut because they can be directly.
highly irritating to the oral and esophageal
Initial Database surfaces. Follow pill with 5-10 mL of Technician Tips
• Serum biochemistry profile: increased total water to reduce risk of esophageal stricture. Demonstrate for owners how to properly
calcium; phosphorus within reference range Liquid formulations are available but may administer medications, including giving water
○ Concurrent CKD associated with azote- not be palatable. afterward to minimize the risk of esophageal
mia, hyperphosphatemia ○ Occasionally, a combination of predniso- stricture with alendronate.
• Ionized calcium: usually mild to moderate lone and alendronate is required to control
increase (80% between 1.5 and 1.75 mmol/L; iCa. Client Education
1.4 mmol/L is the upper end of the reference Proper administration of medications
range) Nutrition/Diet
○ If iCa cannot be measured quickly • High-fiber diet and/or psyllium supplementa- SUGGESTED READING
in house, sample should be collected tion recommended Finch NC: Hypercalcemia in cats: the complexities of
anaerobically and transported on ice. • Wet/canned foods preferred calcium regulation and associated clinical challenges.
○ Exposure of sample to air can lead to loss • Oxalate prevention diets useful for cats with J Feline Med Surg 18:387-399. 2016.
of CO 2, resulting in decreased iCa. no evidence of CKD
○ Lactic acid accumulation alters the pH • Renal diets are appropriate for cats with AUTHOR: Leah A. Cohn, DVM, PhD, DACVIM
EDITOR: Etienne Côté, DVM, DACVIM
of stored samples, resulting in increased concurrent azotemia.
iCa.
• CBC: unremarkable Possible Complications
• Urinalysis: variable urine specific gravity, • Uncontrolled hypercalcemia may result in
possible calcium oxalate crystalluria calcium oxalate urolithiasis.

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