NAC OSCE Clinical Reasoning 2 — Questions and Answers
Question 1: A patient with known type 2 diabetes presents with confusion, rapid breathing, and fruity breath odour. Blood glucose is 28 mmol/L. What is the MOST likely diagnosis?
- Hypoglycemia
- Diabetic ketoacidosis (DKA) — characterized by hyperglycemia, metabolic acidosis, and ketonemia/ketonuria (Correct answer)
- Hyperglycemic hyperosmolar state (HHS)
- Alcohol intoxication
Correct answer: Diabetic ketoacidosis (DKA) — characterized by hyperglycemia, metabolic acidosis, and ketonemia/ketonuria
The triad of hyperglycemia (28 mmol/L), Kussmaul breathing (deep rapid breathing — respiratory compensation for metabolic acidosis), and fruity breath (acetone from ketone production) is classic for DKA. While more common in type 1 diabetes, DKA can occur in type 2 diabetes. Treatment priorities are IV fluids, insulin infusion, and electrolyte replacement (especially potassium).
Question 2: A 60-year-old man presents with progressive dysphagia to solids more than liquids over 3 months, associated with weight loss. What is the MOST concerning diagnosis?
- Gastroesophageal reflux disease
- Esophageal carcinoma — progressive dysphagia to solids with weight loss in an older patient requires urgent endoscopy (Correct answer)
- Achalasia
- Globus pharyngeus
Correct answer: Esophageal carcinoma — progressive dysphagia to solids with weight loss in an older patient requires urgent endoscopy
Progressive dysphagia to solids more than liquids suggests a mechanical obstruction (unlike motility disorders which typically affect solids and liquids equally). Combined with weight loss and age, esophageal carcinoma must be excluded urgently. Upper GI endoscopy with biopsy is the investigation of choice. Risk factors include smoking, alcohol, Barrett's esophagus, and chronic reflux.
Question 3: What is 'anchoring bias' in clinical reasoning and how can it lead to diagnostic error?
- The tendency to order too many tests
- The tendency to focus on the first piece of information or initial diagnosis encountered and fail to adjust the diagnosis adequately when new contradictory information emerges (Correct answer)
- The tendency to always agree with the patient's self-diagnosis
- The tendency to refer every patient to a specialist
Correct answer: The tendency to focus on the first piece of information or initial diagnosis encountered and fail to adjust the diagnosis adequately when new contradictory information emerges
Anchoring bias occurs when a clinician fixes on an initial impression and insufficiently adjusts their diagnosis as new data becomes available. For example, assuming chest pain is musculoskeletal because the patient is young, and missing an acute coronary syndrome when the ECG shows changes. Awareness of cognitive biases and systematic diagnostic approaches (like VINDICATE) help mitigate this.
Question 4: A 35-year-old woman presents with a butterfly-shaped facial rash, joint pain, fatigue, and positive ANA. What condition should be strongly suspected?
- Rosacea
- Systemic lupus erythematosus (SLE) — the malar rash, arthralgia, fatigue, and positive ANA are classic features (Correct answer)
- Contact dermatitis
- Rheumatoid arthritis
Correct answer: Systemic lupus erythematosus (SLE) — the malar rash, arthralgia, fatigue, and positive ANA are classic features
The malar (butterfly) rash sparing the nasolabial folds, combined with arthralgia, fatigue, and positive ANA, is highly suggestive of SLE. Further investigations include anti-dsDNA antibodies (more specific), complement levels (C3/C4), CBC, renal function, and urinalysis (for lupus nephritis). SLE predominantly affects women of childbearing age with a female-to-male ratio of approximately 9:1.
Question 5: A patient with known atrial fibrillation presents with sudden severe abdominal pain but a relatively benign abdominal examination ('pain out of proportion to exam'). What is the MOST likely diagnosis?
- Peptic ulcer disease
- Acute mesenteric ischemia — embolic occlusion of the mesenteric artery, which is a surgical emergency (Correct answer)
- Functional abdominal pain
- Acute pancreatitis
Correct answer: Acute mesenteric ischemia — embolic occlusion of the mesenteric artery, which is a surgical emergency
The classic presentation of acute mesenteric ischemia is severe abdominal pain 'out of proportion to physical examination findings' in a patient with a source of embolism (atrial fibrillation). The lack of peritoneal signs early on is because the ischemia has not yet caused bowel necrosis. CT angiography is the diagnostic test of choice. Mortality is very high (60-80%) if not diagnosed and treated promptly.
Question 6: What are the Canadian Task Force on Preventive Health Care's recommendations for colorectal cancer screening in average-risk individuals?
- No screening is recommended
- Screening with fecal immunochemical test (FIT) every 2 years or flexible sigmoidoscopy every 10 years for adults aged 50-74 (Correct answer)
- Colonoscopy every year starting at age 40
- Screening only for those with a family history
Correct answer: Screening with fecal immunochemical test (FIT) every 2 years or flexible sigmoidoscopy every 10 years for adults aged 50-74
The Canadian Task Force recommends screening average-risk adults aged 50-74 with FIT every 2 years or flexible sigmoidoscopy every 10 years. Colonoscopy is not recommended as a primary screening test for average-risk individuals. Higher-risk individuals (family history, inflammatory bowel disease) follow different screening protocols with earlier initiation and colonoscopy.
NAC OSCE Clinical Reasoning 2
A patient with known type 2 diabetes presents with confusion, rapid breathing, and fruity breath odour.
Blood glucose is 28 mmol/L.
What is the MOST likely diagnosis?