Creating a differential diagnosis list should include consideration of patient history, clinical signs, and physical examination findings to help narrow down the list. Components of a differential diagnosis list may range from general categories of disease (eg, renal disease, adrenal disorders) to more specific etiologies (eg, pyelonephritis, hypoadrenocorticism).
Being an excellent veterinary diagnostician depends on a solid foundation in the basics. In this General Practice Skills series, we’ll tackle a different skill critical to daily practice: history-taking, making a master problem list, compiling differentials, and utilizing heuristics/patterns.
In many cases, creating a differential diagnosis list consists of 2 stages. An initial list of differentials is made based on the patient’s problem list, using information gathered during history-taking and physical examination. This list can then help determine which diagnostic tests are indicated and how they should be prioritized. After some or all diagnostic test results have been compiled, the initial list can be refined, helping determine whether treatment can be initiated, additional diagnostic testing is needed, or a combination of both options should be pursued.
For the following cases, generate 2 differential diagnosis lists, with the first based on the patient history, physical examination, and problem list and the second based on the provided diagnostic test results.
The Case: Unusual Behavior in a Cat
Penelope, a 10-lb (4.5-kg), 9-year-old spayed domestic shorthair cat, is presented for sudden onset of odd behavior, including increased vocalization, reluctance to jump, and lack of play activity, ≈3 days prior to presentation.
History
Penelope is the only animal in the home. She lives primarily indoors but occasionally gets out of the house (most recently, 5 days prior). Flea and tick preventives are not current, and she is not receiving any medication. Vaccines are up to date. She has been fed the same diet for several years. Her owner reports that her appetite appears slightly diminished but there is no vomiting.
Physical Examination
On physical examination, Penelope is quiet, alert, and responsive but reluctant to move around the room. BCS is 5/9, and she has not gained or lost weight compared with an examination 6 months earlier. Temperature is 102.1°F (38.9°C), heart rate is 200 bpm, and respiratory rate is 30 breaths per minute. Skin and coat are in good condition with no signs of external parasites. Abdominal palpation is unremarkable. Both corneas and anterior chambers appear normal, but pupils are mydriatic and minimally responsive to light. Fundic examination reveals multifocal retinal hemorrhages. Menace response is negative bilaterally.
Which of the following should be included on the initial differential diagnosis list for Penelope’s fundic changes?
Diagnostic Testing
A comprehensive panel that includes CBC, serum chemistry profile, total thyroxine (tT4), urinalysis, and retroviral testing is performed. Two-view thoracic and abdominal radiography, assessment of intraocular pressure, and indirect blood pressure measurement via Doppler are also performed.
Findings include a mild neutrophilia and urine specific gravity of 1.040. BUN, creatinine, blood glucose, and tT4 are within normal limits. Radiographs are unremarkable. Systolic blood pressure is 180 mm Hg. Retroviral testing is negative. Intraocular pressure is normal bilaterally.
Which of the following should be included on the refined differential diagnosis list?
Penelope is tentatively diagnosed with idiopathic hypertension, and treatment is initiated pending further testing to rule out coagulopathy and neoplasia. To learn more about how systemic hypertension can affect the eye, see Top 5 Ocular Consequences of Systemic Hypertension.
The Case: Inappropriate Urination in a Dog
Tucker, a 6-year-old, 86-lb (39-kg) neutered male Labrador retriever, is presented for urinating in the house overnight.
History
The owner reports Tucker has been housebroken for several years but began urinating indoors overnight 3 to 4 weeks prior and now does so daily. He is able to go in and out of the house during the day via a dog door. The owner reports Tucker is drinking more water than normal. His appetite is normal to slightly increased; he has not eaten since the night before presentation. Tucker has a history of seasonal allergies. Approximately 1 month prior, his owner started administering prednisone (40 mg total PO every 24 hours) that was remaining from a previous prescription without consulting a clinician.
Physical Examination
On physical examination, Tucker is bright, alert, and responsive. BCS is 7/9. Temperature and heart rate are normal, but Tucker pants throughout the examination. Heart and lungs are normal on auscultation. His coat has increased scale, with hair loss noted on the ventrum and flanks. There is evidence of erythema, pustules, and papules in both axillae and on the ventral abdomen, along with patches of hyperpigmentation. Tucker is tense on abdominal palpation. Blood glucose measured via a point-of-care tool is 180 mg/dL (reference interval, 80-120 mg/dL).
Which of the following should be included on the initial differential diagnosis list for Tucker’s hyperglycemia?
Diagnostic Testing
A comprehensive panel that includes CBC, serum chemistry profile, tT4, and urinalysis is performed. CBC shows a leukocytosis with neutrophilia and lymphopenia. Blood glucose is confirmed elevated at 192 mg/dL (reference interval, 68-110 mg/dL). Other abnormalities include ALP of 299 U/L (reference interval, 8-120 U/L) and ALT of 120 U/L (reference interval, 16-97 U/L). Abdominal radiographs demonstrate mild hepatomegaly with no evidence of urolithiasis. Systolic blood pressure is 170 mm Hg (reference interval, 110-160 mm Hg).
Which of the following should be included on the refined differential diagnosis list?
Tucker is suspected to have iatrogenic hyperadrenocorticism caused by prednisone administration. Prednisone will be tapered, and Tucker will be reassessed following discontinuation of the medication. To learn more about hyperglycemia, see Hyperglycemia: A Complete Guide for Dogs & Cats.
The Case: Chronic Regurgitation in a Puppy
Charlie, a 5-month-old, 21.6-lb (9.8-kg) intact male Siberian husky, is presented for chronic regurgitation after meals.
History
At ≈6 weeks of age, Charlie started regurgitating undigested food 10 minutes to 2 hours after meals. Episodes were occasionally accompanied by coughing and abdominal effort. The owner started feeding smaller meals more often, and episodes became less frequent. Charlie eats an appropriate amount of food based on his age and weight but is thin compared with his littermates. He is not receiving any medication.
Physical Examination
On physical examination, Charlie is alert, responsive, and hydrated. Examination results are within normal limits. BCS is 4/9.
Which of the following should be included on the initial differential diagnosis list for Charlie’s regurgitation?
Diagnostic Testing
PCV, total protein, and whole blood glucose are within normal limits. Right lateral, left lateral, and ventrodorsal thoracic radiography is performed. Ventrodorsal radiographs show left deviation of the trachea just cranial to the cardiac silhouette.
Which of the following should be included on the refined differential diagnosis list?
For more about Charlie’s diagnosis, see Chronic Regurgitation in a Puppy.
Up Next: Heuristics
Making a presumptive diagnosis too quickly may lead to ignoring information that supports the true diagnosis. Explore the final installment in our general practice skills series.