NAVLE General Practice 5

Question 1

A 7-year-old intact male Cavalier King Charles Spaniel presents with a 3-week history of progressive exercise intolerance and a grade IV/VI left apical systolic murmur. Thoracic radiographs reveal moderate left atrial enlargement with pulmonary venous distension but no overt edema. Per EPIC trial criteria, which treatment is most appropriate at this time?

Accepted Answer

Pimobendan 0.25–0.3 mg/kg PO BID

Answer

The EPIC trial demonstrated that pimobendan initiated in the preclinical (Stage B2) phase of myxomatous mitral valve disease — defined by cardiomegaly on radiographs or echocardiography (LVIDDN ≥1.7 or vertebral heart score ≥10.5) — significantly delayed onset of CHF by a median of 15 months. Furosemide is reserved for overt heart failure (Stage C/D). ACE inhibitors and spironolactone are not indicated as monotherapy in B2 per current ACVIM guidelines post-EPIC.

Question 2

A 5-year-old spayed female domestic shorthair cat presents with a 2-day history of open-mouth breathing and severe dyspnea. On auscultation, heart sounds are muffled ventrally and lung sounds are absent in the ventral thorax bilaterally. Thoracocentesis yields 180 mL of milky, white-opaque fluid from each hemithorax. Cytology shows small lymphocytes predominating with a triglyceride concentration greater than serum. What is the most likely underlying etiology in this cat?

Accepted Answer

Idiopathic chylothorax

Answer

Idiopathic chylothorax is the most common cause of chylothorax in cats (~50% of cases). While lymphoma and cardiac disease are differentials, lymphoma would typically show neoplastic lymphocytes on cytology, and HCM-associated chylothorax is relatively rare. The milky fluid with chylomicrons (triglycerides > serum triglycerides) and small lymphocyte predominance is classic chylothorax; without neoplastic cells and with a normal-appearing cardiac silhouette bilaterally, idiopathic etiology is most likely.

Question 3

A 3-year-old Quarter Horse gelding presents for acute onset of right forelimb lameness (grade 4/5) after a barrel racing event. Hoof testers elicit a strong positive reaction over the lateral heel. Perineural anesthesia of the lateral palmar digital nerve abolishes the lameness. Radiographs reveal a thin, radiolucent line through the lateral palmar process of the distal phalanx (P3). Which pathophysiologic mechanism best explains why this specific fracture configuration carries a guarded prognosis for return to competition?

Accepted Answer

Involvement of the distal interphalangeal joint articular surface increasing the risk of degenerative joint disease

Answer

Palmar process (wing) fractures of P3 are classified by Sanders & Stashak. Non-articular fractures carry a good prognosis, but when the fracture line extends into the distal interphalangeal (coffin) joint, articular surface damage predisposes to post-traumatic osteoarthritis, significantly worsening the prognosis for return to high-performance competition. Avascular necrosis is not a primary mechanism in wing fractures. Septic osteitis is a complication of solar penetration wounds, not this fracture type specifically. DDFT tension is more relevant to the middle third fractures.

Question 4

A 6-year-old neutered male mixed-breed dog is presented for polydipsia, polyuria, and muscle weakness. Serum chemistry reveals sodium 158 mEq/L, potassium 2.8 mEq/L, and bicarbonate 30 mEq/L. Blood pressure is 178/110 mmHg. Urine aldosterone-to-creatinine ratio is markedly elevated. An adrenal mass (2.1 cm) is identified on ultrasound. Cortisol concentrations pre- and post-ACTH stimulation are within normal limits. What is the most appropriate next diagnostic step?

Accepted Answer

CT scan of the abdomen to evaluate for vascular invasion and characterize the mass

Answer

This presentation is classic for primary hyperaldosteronism (Conn's syndrome) in a dog — hypertension, hypokalemia, hypernatremia, metabolic alkalosis, and an adrenal mass with normal cortisol dynamics. Once primary hyperaldosteronism is biochemically confirmed (elevated aldosterone:creatinine), the critical next step before surgical adrenalectomy is CT imaging to assess mass characteristics, identify vascular invasion, detect contralateral adrenal involvement, and rule out metastatic disease — all of which dictate surgical candidacy and prognosis. Plasma renin activity is useful but not the most actionable immediate next step given that surgical planning takes priority.

Question 5

A herd of 30 beef cow-calf pairs is experiencing an outbreak of bloody diarrhea in calves 5–21 days of age. Mortality has reached 30% despite oral electrolyte therapy. Post-mortem findings include hemorrhagic enteritis of the jejunum and ileum with villous necrosis and blunting. Gram-positive, spore-forming rods are visualized on intestinal smear. PCR of intestinal contents is positive for NetB toxin gene. Which pathogen and the toxin most responsible for villous destruction are correctly identified?

Accepted Answer

Clostridium perfringens Type C; beta toxin

Answer

NetB toxin is produced by Clostridium perfringens Type C and is a pore-forming toxin. However, the primary virulence factor in Type C hemorrhagic enteritis of neonatal calves is beta toxin (cpb gene), which causes severe necrotizing enteritis by disrupting intestinal epithelium. Beta toxin is protease-sensitive, which is why it preferentially affects neonates lacking tryptic activity. Type A causes mild diarrhea via alpha toxin; Type D causes pulpy kidney/edema disease via epsilon toxin; C. difficile produces toxins A and B in a different syndrome. The NetB gene in the PCR confirms Type C.

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE General Practice 5