Differential Diagnosis for Acute Limb Ischemia

Given the patient's history of diabetes mellitus (DM) and hypertension (HTN), along with right leg pain increased by exertion and an absent popliteal pulse on the right leg, we can approach the differential diagnosis as follows:

• Single Most Likely Diagnosis

  • Chronic Limb Ischemia with Possible Progression to Acute Limb Ischemia: The patient's symptoms of leg pain increased by exertion (intermittent claudication) and the absence of a popliteal pulse are indicative of chronic limb ischemia. However, the presence of pain at rest (if confirmed) could suggest a progression towards acute limb ischemia, which is a medical emergency.

• Other Likely Diagnoses

  • Peripheral Artery Disease (PAD): The patient's history of smoking (40 pack/year) significantly increases the risk for PAD, which can cause intermittent claudication and is consistent with the absent popliteal pulse.
  • Atherosclerotic Disease: Given the patient's history of DM and HTN, along with smoking, atherosclerotic disease is likely contributing to the limb ischemia.

• Do Not Miss Diagnoses

  • Acute Limb Ischemia: This is indicated by C. Evidence of Pain during Rest. Pain at rest, especially if severe and of sudden onset, is a hallmark of acute limb ischemia, which requires immediate medical attention to prevent limb loss.
  • Embolic Event: Although less likely given the chronic nature of the symptoms, an embolic event causing acute limb ischemia must be considered, especially if there's a sudden worsening of symptoms.

• Rare Diagnoses

  • Vasculitis: Conditions like Buerger's disease or other forms of vasculitis could lead to limb ischemia but are less common and typically present with additional systemic symptoms.
  • Thromboangiitis Obliterans: A rare disease of the blood vessels of the arms and legs, which could present similarly but is less common and usually affects younger individuals who smoke.

The key indicator of acute limb ischemia among the provided options is C. Evidence of Pain during Rest, as this symptom suggests a critical reduction in blood flow that requires immediate attention.