Page 1017 - Cote clinical veterinary advisor dogs and cats 4th

500 Hyperparathyroidism, Primary

• A parathyroid mass is not usually palpable within the upper half of the reference range Possible Complications
in dogs but may be palpable in the ventral is inappropriate with concurrent ionized • The most important complication with para-
VetBooks.ir Etiology and Pathophysiology calcemia with a serum PTH concentration • Unaffected parathyroid glands atrophy with
thyroidectomy or ablation is postprocedural
hypercalcemia. Therefore, an ionized hyper-
neck in cats.
hypocalcemia.
that is high or within the upper half of the
• PHPTH is usually due to a solitary parathy-
of PHPTH.
roid adenoma (90%). Less common causes reference limits is consistent with a diagnosis prolonged hypercalcemia. After removal of
affected gland(s), serum PTH and calcium
include hyperplasia of one or more glands • A serum PTH concentration within the lower concentrations may decline to below the
or (rarely) carcinoma. half of the reference range in the face of reference range before remaining normal
• Serum PTH concentration is normally hypercalcemia is suspicious for PHPTH. glands recover.
controlled by blood ionized calcium con- ○ Increased PTH: ≈25% of cases • Hospitalization recommended for 5 days
centrations by negative feedback. In PHPTH, ○ PTH within reference range: ≈75% of after surgery to monitor for signs of hypo-
the gland(s) function autonomously, and cases; of these, more than one-half are calcemia and serum calcium concentrations
feedback inhibition is lost. in the lower half. (q 12-24h).
• Increased PTH causes hypercalcemia and ○ If PTH is in the lower half of the reference • Treatment for hypocalcemia (vitamin
hypophosphatemia. range, further diagnostics are needed to D +/− calcium) must be individualized.
• Clinical signs are due to hypercalcemia determine if PHPTH. Serum calcium concentration should be
(p. 491). • Cervical ultrasonography requires an maintained in the slightly low/low-normal
experienced ultrasonographer and sensitive range (e.g. 8-9.5 mg/dL [2-2.4 mmol/L]) to
DIAGNOSIS equipment. Visualization of an enlarged prevent clinical signs of hypocalcemia while
parathyroid gland(s) in conjunction with stimulating functional recovery of atrophied
Diagnostic Overview compatible serum ionized calcium and PTH parathyroid glands.
• Concurrent hypercalcemia and low to low- concentrations strongly support the diagnosis ○ If serum calcium concentration < 14 mg/
normal serum phosphorus concentration of PHPTH. dL (<3.5 mmol/L) before surgery, postop-
are suggestive of PHPTH; however, these erative hypocalcemia is unlikely. Treatment
findings are also characteristic of humoral TREATMENT is recommended only if total calcium
hypercalcemia of malignancy, a far more falls below 8.5 mg/dL (2.1 mmol/L),
common disorder (p. 754). Presence of cystic Treatment Overview if the rate of decline in calcium after
calculi and/or the absence of clinical signs Goals are to remove or ablate affected tissue surgery is rapid (e.g., > 25% in 1 day)
further increase suspicion for PHPTH. and monitor/treat postoperative hypocalcemia. or clinical signs of hypocalcemia occur
• Parathyroid masses may be visible with ultra- Referral is indicated if the clinician is unfamiliar (p. 515).
sonography; failure to visualize a parathyroid with thyroid/parathyroid evaluation and surgery ○ If clinical hypocalcemia occurs, administer
mass does not rule out the diagnosis. or if 24-hour care and in-house serum calcium 10% calcium gluconate (0.5-1.5 mL/
• The diagnosis is established by measuring monitoring cannot be provided during the kg IV, slowly over 15-30 minutes to
concurrent serum ionized calcium and PTH immediate postprocedural period. effect).
concentrations. ○ If pre-treatment serum calcium concentra-
Acute General Treatment tion > 14 mg/dL (>3.5 mmol/L), begin
Differential Diagnosis • Nonspecific treatment of hypercalcemia while prophylactic vitamin D treatment the
Hypercalcemia (pp. 491 and 1233) awaiting definitive diagnosis or surgery is not morning of surgery.
usually required. A decision to treat is made ○ If pre-treatment serum calcium concentra-
Initial Database based on the presence of clinical signs and tion > 18 mg/dL (>4.5 mmol/L), begin
• CBC, serum biochemical profile, urinalysis, other factors (p. 491). prophylactic treatment 36 hours before
urine culture (if lower urinary signs present): • Treatment of choice is removal/destruction surgery.
hypercalcemia, low or low-normal phospho- of the affected gland(s). Surgical exploration ○ If a patient requires vitamin D, oral
rus concentration, and isosthenuria typical. of the neck with removal and histopathologic calcium supplementation (0.5-1.0 g/day
Azotemia is uncommon. Urinary tract evaluation of the affected tissue is most divided, cats; 1.0-4.0 g/day divided, dogs)
infection (UTI) is common (e.g., bacteriuria, common. Usually, a solitary parathyroid mass should be dispensed (p. 515). Calcium
pyuria). is easily identified and removed. Occasionally, carbonate is preferred; it contains 40%
• Confirm hypercalcemia by repeating the test identification of affected glands is difficult, calcium, so each gram contains 0.4 g of
on a new sample and/or, preferably, measur- and more than one gland may be removed. calcium.
ing serum ionized calcium concentration. • Percutaneous ultrasound-guided ethanol ○ If 1-3 parathyroid glands are removed,
Further testing to determine a cause of ablation and radiofrequency heat ablation vitamin D and oral calcium treatment
hypercalcemia should not be pursued unless are effective and less invasive options but can be tapered over 3-6 months based
ionized hypercalcemia is confirmed. technically challenging and still require on serum calcium levels.
• Formulas to correct serum calcium to account general anesthesia. Both require an expe- ○ Complications after parathyroid ablation
for changes in serum albumin or protein rienced ultrasonographer, and the latter occur uncommonly and include cough,
values are not recommended. requires specialized equipment. voice change, and Horner’s syndrome.
• Abdominal radiographs: possible cystic calculi
• Other tests to rule out more common causes Chronic Treatment Recommended Monitoring
of hypercalcemia, particularly malignancy, • Surgical or ablation therapy is curative in Recurrences may be observed > 12 months
include thoracic radiographs, abdominal most patients, and chronic therapy is not after successful treatment; evaluation of serum
ultrasound, aspiration of lymph nodes and/ required. calcium is recommended q 3-6 months. Due to
or bone marrow, and/or measurement of • If present, hypoparathyroidism and/or the genetic predisposition, recurrence is more
serum parathyroid hormone–related protein hypothyroidism require treatment (pp. 519 likely in affected Keeshonden.
(PTHrP) concentration (p. 1371). and 525).
• Medical therapy (cinalcet) is used in people PROGNOSIS & OUTCOME
Advanced or Confirmatory Testing but is cost-prohibitive in veterinary medicine.
• Concurrent serum ionized calcium and PTH • Address UTI (p. 232) and cystic calculi Prognosis is excellent after successful surgery
concentrations: a serum PTH concentration (p. 1014). or ablation.
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