NAC OSCE Clinical Reasoning — Questions and Answers
Question 1: A 55-year-old male presents with sudden-onset severe headache described as 'the worst headache of my life.' What is the MOST important diagnosis to rule out?
- Tension headache
- Subarachnoid hemorrhage — a life-threatening emergency requiring urgent CT head and, if negative, lumbar puncture (Correct answer)
- Migraine with aura
- Sinusitis
Correct answer: Subarachnoid hemorrhage — a life-threatening emergency requiring urgent CT head and, if negative, lumbar puncture
A sudden-onset severe 'thunderclap' headache is classic for subarachnoid hemorrhage (SAH) until proven otherwise. SAH carries high mortality (up to 50%) and requires urgent non-contrast CT head (95-98% sensitive within 6 hours) followed by lumbar puncture if CT is negative. Missing this diagnosis can be fatal.
Question 2: A 30-year-old woman presents with a unilateral, throbbing headache with nausea and photophobia. She reports seeing zigzag lines before the headache started. What is the MOST likely diagnosis?
- Tension-type headache
- Migraine with aura — the visual symptoms (scintillating scotoma) preceding the headache are characteristic (Correct answer)
- Cluster headache
- Meningitis
Correct answer: Migraine with aura — the visual symptoms (scintillating scotoma) preceding the headache are characteristic
This presentation is classic for migraine with aura: visual aura (zigzag lines/scintillating scotoma) preceding a unilateral throbbing headache, accompanied by nausea and photophobia. The aura typically lasts 20-60 minutes. Important considerations include the use of oral contraceptives (increased stroke risk in migraine with aura) and ruling out more serious causes if this is a first presentation.
Question 3: A patient presents with acute right lower quadrant pain, fever, and rebound tenderness. The initial blood work shows elevated WBC. What is the MOST likely diagnosis and next step?
- Gastroenteritis — prescribe anti-emetics and fluids
- Acute appendicitis — urgent surgical consultation and consider CT abdomen/pelvis for confirmation (Correct answer)
- Irritable bowel syndrome — reassure and discharge
- Renal colic — order renal ultrasound
Correct answer: Acute appendicitis — urgent surgical consultation and consider CT abdomen/pelvis for confirmation
Right lower quadrant pain with fever, rebound tenderness, and elevated WBC is the classic presentation of acute appendicitis. While CT abdomen/pelvis is the most sensitive diagnostic test (sensitivity >95%), the clinical picture may warrant direct surgical consultation. Delay in diagnosis increases the risk of perforation, abscess formation, and peritonitis.
Question 4: A 70-year-old man presents with acute onset of left-sided weakness and slurred speech that began 1 hour ago. What is the time-critical management priority?
- Order a full blood panel and wait for results
- Rapid assessment for stroke using a validated scale, urgent non-contrast CT head to exclude hemorrhage, and consideration of thrombolysis (tPA) within the 4.5-hour window (Correct answer)
- Start antibiotics for possible meningitis
- Schedule an outpatient MRI for next week
Correct answer: Rapid assessment for stroke using a validated scale, urgent non-contrast CT head to exclude hemorrhage, and consideration of thrombolysis (tPA) within the 4.5-hour window
Acute focal neurological deficits suggest stroke — 'time is brain.' The priority is rapid CT head to exclude hemorrhagic stroke, then consideration of IV alteplase (tPA) within 4.5 hours of symptom onset for ischemic stroke. Every minute of delay results in further neuronal death. Endovascular thrombectomy may be considered for large vessel occlusions up to 24 hours.
Question 5: When developing a differential diagnosis, what does the mnemonic 'VINDICATE' stand for?
- Viral, Inflammatory, Neoplastic, Degenerative, Idiopathic, Congenital, Autoimmune, Trauma, Endocrine
- Vascular, Infectious, Neoplastic, Degenerative, Iatrogenic, Congenital, Autoimmune, Trauma, Endocrine/metabolic (Correct answer)
- Various, Important, Notable, Diagnostic, Imaging, Clinical, Assessment, Treatment, Evaluation
- Vascular, Immune, Neurological, Digestive, Inflammatory, Cardiac, Allergic, Toxic, Environmental
Correct answer: Vascular, Infectious, Neoplastic, Degenerative, Iatrogenic, Congenital, Autoimmune, Trauma, Endocrine/metabolic
VINDICATE is a systematic approach to generating differential diagnoses: Vascular, Infectious/Inflammatory, Neoplastic, Degenerative/Deficiency, Iatrogenic/Intoxication, Congenital, Autoimmune/Allergic, Trauma, Endocrine/metabolic. Using this framework ensures you consider all major disease categories and reduce the risk of anchoring bias or premature closure.
Question 6: A 25-year-old woman presents with fatigue, weight gain, cold intolerance, and constipation. Her TSH is elevated and free T4 is low. What is the diagnosis and most common cause in Canada?
- Hyperthyroidism — likely Graves' disease
- Hypothyroidism — most commonly Hashimoto's thyroiditis (autoimmune thyroiditis) in Canada (Correct answer)
- Cushing's syndrome
- Adrenal insufficiency
Correct answer: Hypothyroidism — most commonly Hashimoto's thyroiditis (autoimmune thyroiditis) in Canada
Elevated TSH with low free T4 confirms primary hypothyroidism. In Canada (and other iodine-sufficient countries), the most common cause is Hashimoto's thyroiditis (chronic autoimmune thyroiditis), confirmed by positive anti-TPO antibodies. Worldwide, iodine deficiency is the most common cause, but in Canada, autoimmune thyroiditis predominates.
NAC OSCE Clinical Reasoning
A 55-year-old male presents with sudden-onset severe headache described as 'the worst headache of my life.' What is the MOST important diagnosis to rule out?