Page 954 - Problem-Based Feline Medicine

946 PART 11 CAT WITH AN ABNORMAL GAIT

Hypokalemia results in hyperpolarization of muscle Diagnosis
cell membranes which then require greater stimulus
Diagnosis is made by finding decreased serum potassium
for depolarization, leading to generalized muscle weak-
concentrations (usually < 3.5 mmol/L) in association with
ness.
clinical signs. The severity of signs varies between cats
Hypokalemia occurs when the dietary intake is insuf- when potassium is 2.5–3.5 mmol/L. Below 2.5 mmol/L
ficient to replace urinary and fecal loss. and especially below 2.0 mmol/L, signs are life threat-
ening, with death occurring from respiratory muscle
A major contributing factor to hypokalemia in
failure.
older cats is the inability of the kidney to conserve
potassium. Serum creatine kinase (CK) may be elevated reflecting
the mypoathy associated with hypokalemia.
Acidification of diets to prevent struvite urolithias
increases renal and fecal potassium loss. Electrodiagnostic evaluation is rarely performed.
Abnormalities that may be found include increased
Diets deficient in potassium may induce signs. Clinical
insertional activity, fibrillation potentials and positive
signs occurred in one group of cats fed a vegetarian
sharp waves and some bizarre high-frequency dis-
diet.
charges.
Burmese cats have an inherited hypokalemic myopa-
Muscle biopsies often have minimal change present.
thy producing signs of periodic muscle weakness, with
Mild myonecrosis is possible.
signs first evident before 12 months of age, usually
between 4–12 weeks.
Differential diagnosis
Clinical signs Myasthesia gravis, polymyositis and organophosphate
toxicity can all cause similar clinical signs. Hypokalemia
Signalment is typically aged cats > 8 years or young is readily differentiated from these on serum potassium
Burmese < 1 year (usually 2–6 months). concentration and response to treatment.
Typically there is a history of acute onset of weakness. Rarely snake bite or tick paralysis may cause weakness
However, decreased activity and inappetence are often similar to severe acute signs of hypokalemia. Other
present for weeks to months prior to presentation. clinical signs, history and serum potassium concentra-
tion allow differentiation. Typically, cats with bites
Clinical signs include ventral neck flexion, stiff,
from Brown or Tiger snakes have increased plasma
stilted gait and a reluctance to walk or jump. Typically,
(CK) activity and increased clotting times. Cats with
weak cats do not walk far, but soon sit or lie, flopping
tick bite have increased respiratory effort and a tick is
down, instead of carefully sitting as normal cats do.
usually found with careful searching.
Sensitivity to palpation of larger muscle groups may be
noticed.
Dyspnea occurs when the potassium is very low
Treatment
(2.0–2.5 mmol/L), because of weakness of the respira-
tory muscles. It may occur after fluid administration Supplementation with potassium is essential. Oral sup-
because volume dilution and increased urinary potas- plementation is more effective and is associated with
sium loss induced by diuresis may lead to further wors- fewer complications than intravenous administration.
ening of the hypokalemia. Concurrent and intravenous administration should be
reserved for severely weak cats.
Young Burmese cats are susceptible to this disease,
and potassium depletion may have played a role in the Caution should be used when administering potas-
previously described myopathy of Burmese cats. sium intravenously in fluids, as further decreases in
Transient episodes of weakness may occur beginning serum potassium concentration may occur as a result of
between 2–12 months of age. dilution and enhanced loss of potassium in urine.