NAVLE Canine Internal Medicine 6

Question 1

A 7-year-old intact male Golden Retriever presents with polyuria, polydipsia, bilateral symmetric alopecia, and a pendulous abdomen. CBC shows a mild non-regenerative anemia. Serum chemistry reveals elevated ALP at 850 U/L and hypercholesterolemia. Urine specific gravity is 1.008. Low-dose dexamethasone suppression test (LDDST) shows cortisol at 1.9 µg/dL at 4 hours and 2.1 µg/dL at 8 hours. Which of the following is the most accurate interpretation?

Accepted Answer

The pattern is consistent with adrenal-dependent hyperadrenocorticism (ADH)

Answer

In the LDDST, failure to suppress at 8 hours (cortisol >1.4 µg/dL) confirms hyperadrenocorticism. The key discriminating feature here is that cortisol at 4 hours (1.9 µg/dL) is also elevated without any intermediate suppression. PDH cases classically show >50% suppression at 4 hours (escape phenomenon), while ADH shows no suppression at either time point. Both the 4-hour and 8-hour values exceeding 1.4 µg/dL without the escape pattern strongly suggests an autonomously secreting adrenal tumor (ADH). Abdominal ultrasound to evaluate adrenal size is the appropriate next step.

Question 2

A 4-year-old Labrador Retriever is presented for episodic weakness and collapse after exercise. The owner reports the dog recovers within 10–20 minutes of rest. On examination, the dog is normal between episodes. Serum chemistry and CBC are unremarkable. An ECG during an induced episode shows a wide complex tachycardia at 280 bpm. Which breed-specific genetic mutation is most directly responsible for this presentation?

Accepted Answer

Dynamin 1 (DNM1) gene mutation causing exercise-induced collapse

Answer

Exercise-Induced Collapse (EIC) in Labrador Retrievers is caused by an autosomal recessive mutation in the Dynamin 1 (DNM1) gene, which encodes a GTPase critical for synaptic vesicle recycling. During intense exercise, the dysfunctional DNM1 leads to failure of neuromuscular transmission, resulting in collapse. The wide-complex tachycardia during the episode represents a ventricular arrhythmia secondary to the collapse event, not a primary cardiac disease. MDR1 mutations cause drug sensitivity. PFK deficiency causes hemolytic episodes with exercise but shows marked regenerative anemia. PK deficiency causes chronic hemolytic anemia.

Question 3

A 9-year-old Miniature Schnauzer presents with acute pancreatitis confirmed on abdominal ultrasound and elevated spec cPL. Three days into hospitalization with IV fluids and analgesia, the dog develops icterus. Bilirubin is 8.2 mg/dL (predominantly direct). ALP is 1,200 U/L and GGT is 180 U/L. The dog remains anorexic. Abdominal ultrasound now shows a dilated common bile duct at 6 mm. What is the most likely underlying cause of the new icterus?

Accepted Answer

Extrahepatic biliary obstruction (EHBO) secondary to pancreatic inflammation

Answer

The combination of acute pancreatitis, predominantly direct (conjugated) hyperbilirubinemia, markedly elevated ALP and GGT (cholestatic pattern), and a dilated common bile duct (>5 mm in dogs is abnormal) is classic for extrahepatic biliary obstruction (EHBO). Pancreatic inflammation causes edema and compression of the common bile duct as it traverses the mesoduodenum adjacent to the pancreas. IMHA would cause predominantly indirect (unconjugated) hyperbilirubinemia with spherocytes and a positive Coombs test. Hepatic lipidosis is more characteristic of cats. Opioid-induced sphincter of Oddi spasm can cause mild biliary dilation but typically does not cause this degree of bilirubinemia.

Question 4

A 6-year-old Bernese Mountain Dog presents with progressive exercise intolerance and a 3-week history of ascites. Physical exam reveals jugular venous distension, muffled heart sounds, and hepatomegaly. Echocardiography demonstrates a large pericardial effusion. Pericardiocentesis is performed, yielding 600 mL of serosanguineous fluid. Cytology of the fluid is non-diagnostic. Which of the following is the most common underlying etiology in this breed and age group, and what is the most appropriate long-term management?

Accepted Answer

Right atrial hemangiosarcoma; recommend pericardiectomy plus doxorubicin-based chemotherapy

Answer

In large and giant breeds, particularly Bernese Mountain Dogs, Golden Retrievers, and German Shepherds, right atrial hemangiosarcoma (HSA) is the most common cause of pericardial effusion. Idiopathic pericardial effusion is more common in medium breeds. Aortic body tumors (chemodectoma) are more common in brachycephalic breeds. Hemangiosarcoma carries a very poor prognosis; median survival with pericardiectomy alone is approximately 4 months. Doxorubicin-based chemotherapy (e.g., VAC protocol) is the standard of care adjunct, extending median survival to approximately 4–6 months. Non-diagnostic cytology is typical of HSA, as these tumors shed poorly and hemorrhagic effusions mask neoplastic cells.

Question 5

A 5-year-old male neutered Dachshund presents with acute onset severe abdominal pain, hematemesis, and collapse. PCV is 16% with adequate total protein (6.2 g/dL). Abdominal radiographs show a mild loss of serosal detail. Coagulation panel reveals: PT 28 sec (ref 7–12), PTT 98 sec (ref 60–90), fibrinogen 80 mg/dL (ref 150–400), d-dimers markedly elevated. Platelet count is 40,000/µL. Which of the following best explains this coagulopathy pattern?

Accepted Answer

Disseminated intravascular coagulation (DIC) secondary to a systemic disease process

Answer

The combination of prolonged PT and PTT, thrombocytopenia, markedly elevated d-dimers, and critically low fibrinogen defines DIC (both the procoagulant and fibrinolytic phases). The consumption of clotting factors AND platelets combined with d-dimer elevation (cross-linked fibrin degradation products) is the hallmark. Rodenticide toxicity causes prolonged PT (extrinsic pathway factor VII is shortest half-life) but does NOT cause thrombocytopenia or elevated d-dimers or hypofibrinogenemia. Hemophilia A causes isolated PTT prolongation. Aspirin causes platelet dysfunction (prolonged closure time/buccal mucosal bleeding time) but not this global consumptive coagulopathy. The acute abdomen with hematemesis suggests an underlying trigger (splenic mass rupture, sepsis, or neoplasia) driving the DIC.

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE Canine Internal Medicine 6