Disorders of the Parathyroid Gland

Question 1

describe calcium homeostasis

Answer 1

1. Ca is stored in bone; absorbed or excreted by SI and kidneys
2. 4 main hormones:
   -PTH
   -parathyroid hormone-related protein (PTHrP)
   -vitamin D (calcitriol)
   -calcitonin
3. calcium sensing receptor (CaSR): located in parathyroid glands, cartilage, bone, and kidneys
4. PTH:
   -released in response to hypocalcemia
   -increase blood calcium via increased tubular reabsorption, increased bone resportion, increased production of calcitriol
5. calcitriol:
   -absorbed in GI, transported to liver, transported to kidneys
   -hydroxylation occuring constantly but final step depends on Ca and PTH levels
   -increase blood Ca by enhancing GI absorption and promoting bone formation
6. calcitonin:
   -produced in thyroid gland
   -released secondary to hypercalcemia
   -inhibits osteoclastic activity and decreases tubular reabsorption

Question 2

describe the parathyroid gland

Answer 2

1. 4 glands:
   -2 cranial, external
   -2 caudal, internal
2. chief cells produce PTH
   -small amount constantly secreted
   -bolus secretions in response to hypocalcemia or low calcitriol (active form of vitamin D)

Question 3

describe calcium measurement (not on test but for life)

Answer 3

1. must be measured in heparanized plasma or serum
   -red or green top tubes = GOOD
2. EDTA or citrate chelate calcium will give wildly inaccurate results
   -purple or blue top tubes = BAD
3. hypoalbuminemia lowers TOTAL calcium, NOT ionized calcium

Question 4

describe hypercalcemia clinical signs

Answer 4

depend on severity of hyeprcalcemia

1. common:
   -PU/PD (dogs)
   -anorexia
   -constipation
   -lethargy/weakness
2. less common/more severe:
   -ataxia
   -dull mentation
   -muscle twitching
   -seizures

but MUST CONFIRM HYPERCALCEMIA WITH AN IONIZED CALCIUM

Question 5

describe differential diagnoses for hypercalcemia (HOGS IN YARD)

Answer 5

H: hyperparathyroidism
O: osteolysis
G: granulomatous disease
S: spurious

I: iatrogenic or idiopathic (cats)
N: neoplasia

Y: youth
A: Addison’s disease
R: renal disease
D: vitamin D toxic ity

MUST CONFIRM HYPERCALCEMIA WITH AN IONIZED CALCIUM

Question 6

describe physical exam when see/suspect hypercalcemia

Answer 6

1. depends on underlying cause and severity:
   -dehydration
   -cardiac arrhythmias
   -dull mentation
2. DO A RECTAL EXAM
3. PALPATE LYMPH NODES

Question 7

describe diagnostics when see/suspect hypercalcemia

Answer 7

1. initial diagnostics:
   -CBC
   -serum chemistry
   -urinalysis
   -thoracic radiographs
   -abdominal imaging (rads or US)
2. advanced diagnostics:
   -PTH panel (MSU, includes ionized calcium, PTH, PTHrP)
   -neck US
   -FNA of LN or masses

Question 8

describe primary hyperparathyroidism

Answer 8

1. may present symptomatic or incidental
   -clinical signs vary
2. presumptive vs. definitive diagnosis
   -ionized hypercalcemia
   -low/normal phosphorous
   -low USG
   -HIGH PTH!!
3. most common cause is parathyroid adenoma
   - >90% of cases in dogs only have one of the 4 parathyroid glands affected
4. generally mid-normal or higher concentration of PTH with a significantly elevated iCa

Question 9

describe treatment for primary hyperparathyroidism

Answer 9

1. short term: target hypercalcemia
   -IV fluids: 0.9% NaCl (Na = 154mEq/L and Cl = 154mEq/L, supraphysiologic amount of cloride which is an acid so could make patients acidotic! but chloride promotes calcium excretion so need it!)
   -glucocorticoids: decrease absorption, increase excretion
   -diuretics (furosemide): increase excretion
2. long term: target parathyroid gland
   -surgery: parathyroidectomy
   -ethanol ablation
   -heat ablation

REMEMBER: we treat the patient, not the numbers! unless they are going to start mineralizing organs
-when Ca x Phos = > 60 patient will mineralize organs

Question 10

describe post-op hypocalcemia

Answer 10

1. risk related to degree of pre-op hypercalcemia
   -lower risk if total Ca <14mg/dL or iCa <1.6 mmol/L
2. suggested protocol if tCa <14 mg/dL
   -wait and see approach
   -few days of monitoring post op
   -Ca supplementation if needed (TUMS)
3. suggested protocol if tCA >14 mg/dL
   -acute crisis: calcium gluconate
   -short term: calcitriol
   -calcium supplementation

Question 11

describe clinical signs of hypocalcemia

Answer 11

1. depend on acute or chronic nature and severity of hypocalcemia
2. dogs:
   -tCa <8mg/dL
   -iCa <1.5mmol/L
3. cats:
   -tCa <7mg/dL
   -iCa <1.1mmol/L
4. common:
   -none or
   -muscle tremors of fasciculations
   -facial rubbing
   -muscle cramping
   -stiff gait
   -behavioral change: restlessness or agitation, aggression, hypersensitivity to simuli, disorientation
5. occasional:
   -seizures
   -panting
   -pyrexia
   -lethargy
   -anorexia
   -3rd eyelid prolapse (cats)
   -posterior lenticular cataracts
   -tachycardia or ECG alterations
6. uncommon:
   -PU/PD
   -hypotension
   -respiratory arrest or death

MUST CONFIRM WITH IONIZED CALCIUM

Question 12

list differential diagnoses for hypocalcemia

Answer 12

1. hypoalbuminemia (total hypocalcemia)
2. hypoparathyroidism: primary or secondary
3. renal disease (acute or chronic)
4. pancreatitis
5. ethylene glycol
6. phosphate enema
7. eclampsia

MUST CONFIRM WITH IONIZED CALCIUM

Question 13

describe diagnostics for hypocalcemia

Answer 13

initial:
1. CBC
2. serum
3. urinalysis
4. thoracic radiographs
5. abdominal imaging (rads or US)

Question 14

describe hypoparathyroidism

Answer 14

usually immune-mediated so need supplementation for life (TUMS in food for life, dogs usually do very well with this)

less common than hyperparathyroidism