Differential Diagnosis

• Single most likely diagnosis
  • Vasovagal syncope: This is the most likely diagnosis given the patient's symptoms of loss of consciousness triggered by standing up after passing a dark, watery stool, which suggests a vasovagal response to a gastrointestinal event. The presence of diarrhea, dark stools, and a positive test for occult blood further supports this diagnosis, as it indicates gastrointestinal bleeding, which can lead to hypovolemia and subsequently trigger a vasovagal response.
• Other Likely diagnoses
  • Orthostatic hypotension: Given the patient's symptoms of inability to stand, low blood pressure (82/60 mm Hg), and high pulse rate (150/min), orthostatic hypotension is a plausible diagnosis. The patient's recent history of diarrhea and dark stools could have led to dehydration and hypovolemia, contributing to orthostatic hypotension.
  • Hypoglycemia: Although not directly indicated by the symptoms provided, hypoglycemia can cause loss of consciousness and should be considered, especially if the patient has a history of diabetes or is on medications that could affect blood sugar levels.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Pulmonary embolus: Despite the lungs being clear to auscultation, pulmonary embolism is a critical diagnosis that should not be missed, especially given the patient's recent history of deep venous thrombosis and warfarin therapy. The symptoms of loss of consciousness and tachycardia could be indicative of a pulmonary embolism.
  • Aortic stenosis: The presence of a grade 2/6 systolic murmur could suggest aortic stenosis, which is a serious condition that can lead to syncope, especially exertional syncope. However, the context of the patient's symptoms (occurring after standing up and passing a stool) makes this less likely.
  • Seizure: Although less likely given the context, a seizure could cause loss of consciousness and should be considered, especially if there are any focal neurological deficits or if the loss of consciousness was not immediately preceded by a clear precipitating event.
• Rare diagnoses
  • Carotid sinus hypersensitivity: This condition can cause syncope but is less common and typically associated with neck movements or pressure.
  • Conversion reaction: Now more commonly referred to as a functional neurological symptom disorder, this would be an unusual presentation for a conversion disorder.
  • Hypertrophic obstructive cardiomyopathy: This condition can cause syncope, typically exertional, and is less likely given the context of the patient's symptoms.
  • Mitral valve prolapse: While mitral valve prolapse can be associated with syncope, it is less common and not directly suggested by the patient's symptoms or the physical examination findings provided.
  • Vertebrobasilar insufficiency: This condition can cause loss of consciousness but is typically associated with other neurological symptoms or signs of brainstem or cerebellar dysfunction, which are not mentioned in the scenario.