Small Animal Internal Medicine Flashcards

A 7-year-old intact female Rottweiler presents with polyuria, polydipsia, and a purulent vaginal discharge. CBC reveals a leukocytosis of 42,000 cells/µL with a left shift. Abdominal radiographs show a markedly distended uterus. After emergency ovariohysterectomy and 48 hours of IV antibiotics, the dog develops persistent oliguria despite aggressive fluid therapy. Urine specific gravity is 1.010 and urine sodium is 68 mEq/L. What is the most likely cause of the persistent oliguria?

Answer: Acute tubular necrosis secondary to sepsis-induced renal ischemia

The combination of isosthenuria (USG 1.010), high urine sodium (>40 mEq/L indicating tubular dysfunction — normal tubules would reabsorb sodium), oliguria despite aggressive fluid therapy, and a septic history is classic for acute tubular necrosis (ATN). Sepsis causes renal ischemia via decreased cardiac output, microvascular thrombi, and inflammatory mediator release. Pre-renal azotemia would show urine sodium <20 mEq/L and respond to fluids. Glomerulonephritis typically causes proteinuria rather than oliguria acutely. Medullary washout would not explain oliguria or elevated urine sodium.

A 4-year-old male neutered Doberman Pinscher presents for evaluation of exercise intolerance and a 2-episode history of syncope. Echocardiography reveals a dilated left ventricle with an internal diameter in diastole (LVIDd) of 6.8 cm, fractional shortening of 14%, and spontaneous echo contrast ('smoke') in the left atrium. No mitral regurgitation murmur is auscultated. Which hemostatic abnormality is MOST directly responsible for the increased thromboembolic risk in this patient?

Answer: Blood stasis within the dilated left atrium promoting thrombus formation

Dobermans with dilated cardiomyopathy (DCM) are at high risk for left atrial thrombus formation. The spontaneous echo contrast ('smoke') is a direct echocardiographic sign of blood stasis — red cell rouleaux formation and platelet aggregation occur when blood moves slowly through a large, poorly contracting chamber. This fulfills Virchow's triad (stasis + endothelial dysfunction from wall stretch + hypercoagulable state). While antithrombin III can be depleted in severe hepatic congestion, this is not the primary mechanism. The absence of a murmur despite severe LV dilation is a classic DCM finding — the ventricle dilates uniformly without mitral leaflet distortion initially.

A 9-year-old spayed female Bichon Frise is referred for refractory hypoglycemia. Fasting glucose is 38 mg/dL. Insulin level drawn simultaneously is 28 µIU/mL (reference: 5–20). Abdominal ultrasound is unremarkable. CT scan reveals a 0.8 cm nodule in the right limb of the pancreas. The dog undergoes partial pancreatectomy. Histopathology confirms an insulinoma. Two weeks post-operatively, the owner reports that the dog is now polyuric/polydipsic and has a glucose of 380 mg/dL. What is the most likely explanation?

Answer: Diabetes mellitus secondary to β-cell atrophy from chronic hypoglycemia-induced suppression of normal islet cells

This is a well-recognized but frequently missed complication of insulinoma resection: post-operative diabetes mellitus. The tumor's chronic autonomous insulin secretion causes persistently low blood glucose, which suppresses normal pancreatic β-cells via negative feedback. After tumor removal, the suppressed normal β-cell population cannot immediately upregulate insulin production, resulting in transient or permanent diabetes mellitus. This phenomenon can last weeks to months. While stress hyperglycemia and iatrogenic causes are possible, the persistence (two weeks) and classic presentation point to β-cell suppression. This is analogous to post-surgical hypoadrenocorticism seen after adrenal tumor removal.

A 6-year-old male neutered Labrador Retriever presents with a 3-week history of weight loss, polyphagia, and intermittent large-bowel diarrhea with hematochezia. Physical examination reveals peripheral lymphadenopathy and a thickened colon on rectal examination. Colonoscopy shows diffuse, irregular mucosal thickening. Biopsies demonstrate large granular lymphocytes infiltrating the lamina propria with loss of mucosal architecture. Immunohistochemistry is positive for CD3 and negative for CD20. Flow cytometry shows a CD8+ predominant population. What is the most accurate diagnosis?

Answer: Alimentary lymphoma, T-cell type (epitheliotropic)

The combination of large granular lymphocytes, CD3 positivity (T-cell marker), CD20 negativity (rules out B-cell), and a CD8+ dominant population on flow cytometry is diagnostic of T-cell lymphoma — specifically the epitheliotropic form affecting the GI tract. In dogs, alimentary lymphoma is far more commonly T-cell than B-cell (opposite of cats). T-cell GI lymphoma carries a significantly worse prognosis than B-cell type, with poor response to CHOP protocol. Lymphocytic-plasmacytic enterocolitis would show mixed plasma cells and small lymphocytes without the architectural destruction. Histiocytic ulcerative colitis (Boxer/French Bulldog breed predisposition) would show PAS-positive macrophages, not lymphocytes.

A 5-year-old spayed female Standard Poodle presents for acute collapse. On examination: HR 220 bpm, weak femoral pulses, mucous membranes pale, CRT 3 seconds. ECG shows a wide-complex tachycardia with a rate of 220 bpm. Blood pressure is 60/40 mmHg. The QRS complexes have a right bundle branch block morphology and are preceded by no discernible P-waves. Potassium is 2.9 mEq/L. Which intervention carries the HIGHEST risk of precipitating ventricular fibrillation in this patient?

Answer: Unsynchronized defibrillation at 4 J/kg

Unsynchronized (asynchronous) defibrillation delivers a shock without regard to where in the cardiac cycle the shock lands. If the shock falls during the 'vulnerable period' of ventricular repolarization (the T-wave, corresponding to the relative refractory period), it can precipitate ventricular fibrillation — the 'R-on-T phenomenon.' For a patient with a perfusing (though hemodynamically compromised) organized rhythm, synchronized cardioversion is the correct electrical intervention because it times the shock to the QRS complex. Unsynchronized mode is only appropriate for VF (already disorganized rhythm) or pulseless VT. Lidocaine and procainamide are first-line antiarrhythmics for ventricular tachycardia. The hypokalemia increases risk but is not the intervention in question.

A 10-year-old spayed female Golden Retriever is evaluated for a 6-month history of progressive truncal alopecia, hyperpigmentation, and weight gain without polyuria or polydipsia. UCCR (urine cortisol:creatinine ratio) is normal. A low-dose dexamethasone suppression test (LDDST) shows adequate suppression at 4 hours but escape (cortisol rises above baseline) at 8 hours. ACTH stimulation test is normal. Abdominal ultrasound reveals bilateral adrenal gland size within normal limits. What is the most likely diagnosis?

Answer: Sex hormone-secreting adrenocortical tumor

This is an advanced pattern recognition question. The LDDST 'escape' pattern (suppression at 4 hours, then cortisol rises above baseline at 8 hours) is sometimes misinterpreted as PDH. However, the key discriminators are: (1) normal UCCR argues against cortisol excess, (2) normal ACTH stimulation test is inconsistent with cortisol-secreting tumors (which would show exaggerated response), (3) no PU/PD despite skin changes, and (4) normal adrenal size. Sex hormone-secreting adrenocortical neoplasms (producing progesterone, androstenedione, or 17-hydroxyprogesterone) cause 'atypical Cushing's' — skin changes without cortisol excess. These hormones do not suppress on LDDST because the test only assesses cortisol, and they can cause LDDST escape artifacts. Diagnosis requires a sex hormone panel. Hypothyroidism would show thyroid-specific findings and would not cause LDDST escape.