Page 343 - Problem-Based Feline Medicine

18 – THE THIN, INAPPETENT CAT 335

Small and/or irregular kidneys may be palpable, Renal secondary hyperparathyroidism is character-
occasionally kidneys are enlarged (for example in neo- ized by excess circulating concentrations of parathy-
plastic or cystic kidney disease). roid hormone (PTH) resulting from altered mineral
homeostasis in renal failure, and is present
in approximately 80% of cats with chronic renal
Diagnosis
failure.
Diagnosis is based on demonstration of persistently ● Chronically increased PTH concentrations are toxic
decreased renal excretory function. to the kidney and contribute to ongoing loss of renal
● Persistently elevated blood urea and creatinine function.
concentrations (azotemia) are indicative. ● Factors involved in the pathogenesis of renal hyper-
● Chronicity and stability is based on two assess- parathyroidism leading to increased PTH concen-
ments, ideally at a 2–4 week interval. trations include phosphate retention with declining
glomerular filtration rate, hypocalcemia and
Diagnosis is further supported by demonstration of
decreased synthesis of 1,25-dihydroxycholecalci-
tubular dysfunction:
ferol (calcitriol) by proximal tubular cells.
● Urine specific gravity of less than 1.030 (typi-
● Diagnosis is based on elevated PTH concentrations
cally less than 1.020).
in a cat with chronic renal failure, and normal or
Any factors contributing to the progression of the slightly low serum calcium concentrations.
renal failure, including the initiating disease, and Measurement of ionized calcium is a better indica-
any systemic complications of renal failure should tor of calcium levels than total calcium. Cats with
be identified by diagnostic tests. chronic renal failure and hyperphosphatemia will
be hyperparathyroid.
Attempt to identify the renal disease initiating the fail-
– Samples for PTH assay require special handling,
ure using all or any of the following tests:
therefore contact the diagnostic laboratory.
● Routine hematology and biochemistry.
● Hypokalemia occurs in many cats (20–30%)
● Routine urinalysis (including microscopic sediment
with polyuric renal failure.
examination).
● Hypokalemia may be a consequence or cause of
● Assessment of proteinuria by urine protein:creati-
chronic renal failure in the cat.
nine ratio. Proteinuria is typically very low (1.5–2
● The mechanism is unknown but increased renal
times increase in protein excretion), unless there is
losses of potassium, decreased dietary intake and
significant glomerular disease.
decreased gastrointestinal absorption are implicated.
● Quantitative urine bacterial culture.
● Clinical signs of inappetence and generalized mus-
● Imaging, either radiography to assess renal size and
cle weakness (such as ataxia, inability to jump,
shape, and/or ultrasound examination to assess
stiff, stilted gait and ventroflexion of the neck) may
renal architecture.
occur.
● Renal cytology (fine needle aspiration biopsy) and
biopsy. Normochromic, normocytic, nonregenerative anemia
– However, due to the high risk and low diagnos- is common when chronic renal failure is advanced.
tic yield of histopathology in CRF, biopsy is ● Occurs mainly from relative erythropoietin defi-
rarely indicated unless atypical features such as ciency, but other factors contribute, such as
renomegaly, proteinuria or hematuria are pres- decreased red cell life span, uremic suppression of
ent. Biopsy is only indicated in cases where erythropoiesis and gastrointestinal blood loss.
the result of histopathology will influence the ● Routine hematology should be used to monitor ane-
treatment options and therefore, outcome of mia and rule out other causes.
the case.
Systemic hypertension is present in many cats with
Secondary hyperperathyroidism, hypokalemia, anemia chronic renal failure.
and systemic hypertension are all possible complica- ● Diagnosis is based on serial blood pressure meas-
tions of chronic renal failure. urements.