NAC OSCE Clinical Reasoning 2

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?

Accepted Answer

Diabetic ketoacidosis (DKA) — characterized by hyperglycemia, metabolic acidosis, and ketonemia/ketonuria

Answer

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?

Accepted Answer

Esophageal carcinoma — progressive dysphagia to solids with weight loss in an older patient requires urgent endoscopy

Answer

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?

Accepted 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

Answer

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?

Accepted Answer

Systemic lupus erythematosus (SLE) — the malar rash, arthralgia, fatigue, and positive ANA are classic features

Answer

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?

Accepted Answer

Acute mesenteric ischemia — embolic occlusion of the mesenteric artery, which is a surgical emergency

Answer

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.

NAC OSCE Practice Test

NAC OSCE Practice Test

NAC OSCE Clinical Reasoning 2