Page 253 - Problem-Based Feline Medicine

15 – THE CAT WITH POLYURIA AND POLYDIPSIA 245

Classical signs—Cont’d HYPERCALCEMIA
(HYPERCALCEMIA ASSOCIATED WITH
● Decreased activity and inappetence for
weeks to months. MALIGNANCY, CHOLECALCIFEROL
● Dyspnea in severe cases. TOXICITY, CHRONIC RENAL FAILURE,
● Signs relating to the underlying disease, HYPERPARATHYROIDISM
e.g. polyuria and polydipsia in chronic AND IDIOPATHIC)
renal failure.
Classical signs
● Occurs in older cats and Burmese kittens.
● Anorexia and lethargy.
See main reference on page 893 for details (The Cat ● Vomiting.
With Neck Ventroflexion). ● Weight loss.
● Dysuria, inappropriate urination,
pollakiuria, stranguria.
Clinical signs ● Respiratory signs.
● Lymphadenopathy.
Acute onset of weakness. However, decreased activity ● Palpable cervical mass.
and inappetence are often present for weeks to months
prior to presentation.
Pathogenesis
Ventral neck flexion, stiff, stilted gait, and a reluc-
Calcium is important for formation of bones and
tance to walk or jump are typical.
teeth, and is essential for blood coagulation. It is
Larger muscle groups may appear sensitive or palpa- important for muscle function, including cardiac mus-
tion. cle, as well as nervous system function where it stabi-
lizes nerve cell membranes. As a cation, it is important
Dyspnea occurs when the potassium is very low
for cell membrane permeability.
(2.0–2.5 mmol/L), because of weakness of the respira-
tory muscles. It may occur after fluid administration Calcium is regulated in the body via:
because volume dilution and increased urinary potas- ● Gastrointestinal absorption.
sium loss induced by diuresis may lead to further wors- ● Renal excretion.
ening of the hypokalemia. ● Binding to plasma proteins.
● Tissue deposition, especially into bone.
Polyuria, polydipsia may result from hypokalemia or
be the result of the underlying disease causing Parathyroid hormone (PTH) and calcitriol (active
hypokalemia, such as renal failure or hyperthryoidism. form of vitamin D) maintain calcium homeostasis.
Serum calcium concentration regulates parathyroid
hormone secretion and their serum concentrations have
Diagnosis an inverse linear relationship.
● PTH is produced in the parathyroid gland and
Decreased serum potassium concentrations (usually
acts to increase serum calcium. It stimulates bone
< 3.5 mmol/L) in association with clinical signs are
resorption by increasing osteoclastic activity, which
required for diagnosis. The severity of signs varies
mobilizes calcium into the bloodstream. PTH pro-
between cats when potassium is 2.5–3.5 mmol/L.
motes renal reabsorption of calcium and excretion
Below 2.5 mmol/L and especially below 2.0 mmol/L,
of phosphorus.
signs are life threatening, with death occurring from
● Cholecalciferol (vitamin D) is a fat-soluble vita-
respiratory muscle failure.
min that is metabolized by the liver and kidney to
Serum creatine kinase (CK) may be elevated reflecting produce calcitriol (1,25 [OH] vitamin D), which
2
the mypoathy associated with hypokalemia. acts to increase serum calcium. Calcitriol enhances