Chronic hypokalemia and myonecrosis in a 9 year old female spayed cat

Clinical History

A 9 year old female spayed cat was presented to the Neurology Department of the VCA Veterinary Specialty Center of Seattle following an episode of collapse at home. The cat had been slightly lethargic a few days prior to admission and was unable to lift its head up. Difficulty walking and falling over after a few steps was also reported. Laboratory evaluations performed by the referring veterinarian showed hypokalemia at 3.6 meq/l (reference 4.0-5.8), hypophosphatemia at 3.1 mg/dl (reference 3.5-6.1), and normal thyroid values.

Physical Examination

With the exception of marked cervical ventroflexion and mild generalized weakness, the physical examination was normal. A wide-based stance with head excursions to the left and right was noted. Conscious proprioception and spinal reflexes were normal. The cat was uncomfortable with palpation of the head and cervical spine. Neuroanatomic localization was consistent with a neuromuscular disease or less likely bilateral peripheral vestibular disease.

Diagnostic Tests

CBC and Chemistry Panel
Creatine kinase (CK) activity – 2551 IU/L (reference 56-529) rising in two days to 19,170 IU/L
Electrolytes – Persistent hypokalemia with values ranging from 3.4-3.9 meq/L (reference 4-5.8)
Urinalysis – Specific gravity 1.024 with 2+ protein
Urine microalbumin – 17.8 mg/dl (reference <2.5)
Infectious diseases – Negative for FIV, FeLV, Toxoplasma IgG negative, IgM positive at 1:64
Thoracic radiographs – No significant abnormalities noted
Abdominal ultrasound – The left adrenal gland was enlarged (Fig. 1A, arrow) and irregular suggesting a primary left adrenal tumor or possibly Cushing’s disease. The left kidney was small and irregular with two hypoechoic nodular areas extending off the caudal pole. The right adrenal (Fig. 1B, arrow) was within the normal limits.

Figure 1A Left Adrenal

Figure 1B Right Adrenal

Edrophonium chloride challenge– Negative
Electromyography – Mildly increased insertional activity in the left cranial tibial muscle but otherwise normal
Muscle biopsies – Biopsies were collected under general anesthesia from the triceps, cleidocervicalis and vastus lateralis muscles. The predominant pathological change was myonecrosis (Fig. 2) that was most marked in the cervical muscle.

Figure 2. Modified Gomori trichrome stained fresh frozen biopsy section from the cleidocervicalis muscle showing scattered necrotic fibers with some undergoing phagocytosis. Scattered necrotic fibers were present throughout the biopsy sections of all muscles but were most marked in the cervical muscle. Lymphocytic infiltrates, consistent with myositis (immune-mediated or infectious) were not observed.

Aldosterone (Pre and Post ACTH, Test performed at Michigan State University)
Aldosterone baseline – 1165 pmol/L (reference 198-388)
Aldosterone 1 hr post ACTH – 1406 pmol/L (reference 277-721)
Blood pressure – 145-166 mm/Hg systolic (feline reference 100-150)

Diagnosis and Outcome

At the time of discharge and prior to receipt of aldosterone levels and muscle biopsy results, differentials included hyperaldosteronism secondary to an adrenal tumor, hypokalemia secondary to kidney disease, or generalized myositis (infectious or immune-mediated). Initial treatments included Tumil-K for potassium supplementation, prednisone 5 mg twice daily and Clindamycin 75 mg twice daily. On recheck examination 10 days following discharge, the cat was reported as doing well at home and back to a normal energy level. Ventroflexion of the neck was no longer evident and the cat was ambulatory without fatigue. Following confirmation of hyperaldosteronism and considering the asymmetry of the adrenal glands, an adrenal tumor was suspected. As the cat was doing well clinically and surgical removal of an adrenal tumor may be a risky procedure, medical management with potassium-sparing diuretics (spironolactone 12.5 mg once daily), potassium supplementation (Tumil-K 10 mEq daily) and subcutaneous fluids containing 20 mEq KCl per liter (100 ml given daily) was chosen with periodic monitoring of potassium levels and systolic blood pressure. Myonecrosis in this case was most likely a result of hypokalemia.