This patient presents with signs of acute compartment syndrome (pain out of proportion, paresthesia, pallor, swelling, decreased pulses, and dark urine indicating rhabdomyolysis). Measuring compartment pressures is the diagnostic test of choice to confirm the diagnosis and guide urgent surgical fasciotomy.
Toronto Notes 2023 - Orthopedics:
"Acute compartment syndrome should be suspected in any patient with severe extremity pain, swelling, sensory deficits, and tense compartments. Confirm with compartment pressure measurements. Fasciotomy is indicated if pressure is >30 mmHg or within 30 mmHg of diastolic pressure." MCCQE1 Objectives (Surgery > 51-2: Limb Trauma):
"Candidates must diagnose acute compartment syndrome and initiate appropriate surgical referral after confirming with pressure measurements." Angiography and Doppler studies assess vascular compromise but are not the first step in suspected compartment syndrome. Fixing the hip (C) and testing myoglobin (E) are not diagnostic steps.

Comprehensive and Detailed Explanation:
Decreased libido in elderly patients can be multifactorial, but depression is a common and important cause that must be ruled out before hormone therapy or other steps. A proper mental health screen should precede further interventions.
Toronto Notes 2023 - Psychiatry / Geriatrics:
"In elderly men, reduced libido may be linked to depression, medical illness, or medications. Depression screening is essential." MCCQE1 Objectives (Psychiatry > 71-1: Mood Disorders / Sexual Health):
"Candidates must consider depression as a common cause of decreased libido and assess accordingly before initiating hormone therapy." Testosterone testing (D) may follow. Prescribing (C) is premature. Couples counselling (B) may help if interpersonal issues are identified. Interviewing together (A) may inhibit disclosure.
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The presentation is highly suspicious for acute aortic dissection - sudden chest/back pain and mediastinal widening on chest x-ray. The most definitive and widely available test is contrast-enhanced computed tomography (CT) of the chest.
Toronto Notes 2023 - Cardiology, Aortic Dissection:
"CT angiography of the chest is the gold standard for stable patients with suspected aortic dissection. Look for mediastinal widening on chest x-ray as a clue." MCCQE1 Objectives - Internal Medicine > Cardiovascular Disease:
"Candidates should recognize acute aortic dissection and select appropriate imaging, such as CT chest, for diagnosis in stable patients." Transthoracic echo (A) may miss dissections. ECG (C) helps rule out MI but not dissection. V/Q scan (D) and pulmonary angiography (E) are for suspected pulmonary embolism.

In a patient with known diverticular bleeding and no red flags (e.g., weight loss, anemia, family history), repeating colonoscopy is not required. Diverticular bleeding is typically self-limited. Colonoscopy within the past few years with clear findings suffices.
Toronto Notes 2023 - Gastroenterology, Lower GI Bleed:
"Patients with known diverticulosis and self-limited bleeding who have had prior complete colonoscopy do not require repeat endoscopy unless symptoms recur or persist." MCCQE1 Objectives - Internal Medicine > Gastroenterology:
"Candidates must recognize when no further invasive investigation is necessary in elderly patients with known benign findings and resolved symptoms." Option E is considerate but not clinically necessary for independent patients. Options A, B, and D are not indicated in resolved, low-risk cases.

The symptoms - visual hallucinations, attention deficits, gait instability - suggest dementia with Lewy bodies (DLB), which may show bilateral frontal or parietal atrophy on imaging.
Toronto Notes 2023 - Psychiatry, Neurocognitive Disorders:
"DLB presents with fluctuating cognition, visual hallucinations, parkinsonism, and attention deficits. Imaging may show frontal or parietal atrophy but is not always specific." MCCQE1 Objectives - Psychiatry > Neurocognitive Disorders:
"Candidates must recognize the characteristic features of DLB and support diagnosis with imaging when appropriate." Cerebellar atrophy (A) is linked to ataxia but not hallucinations. Subdural hematoma (B) causes abrupt decline. Mediotemporal atrophy (D) is typical of Alzheimer's. Option E is incorrect - imaging can support the diagnosis.