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Difficulty: HardCardiothoracic and Vascular Surgery

A 68-year-old male with a 20-year history of poorly controlled type 2 diabetes mellitus and chronic kidney disease presents to the vascular surgery clinic due to progressive, severe pain in his right foot. The pain has been present for four weeks, worsens at night when he is lying in bed, and improves significantly when he sits on the edge of the bed and dangles his legs. Physical examination reveals a cool, pale right foot with a 1-cm, shallow, dry, well-demarcated ulcer on the tip of the great toe. No surrounding erythema, warmth, or purulent exudate is noted. The right femoral pulse is palpable, but the popliteal, dorsalis pedis, and posterior tibial pulses are nonpalpable. A bedside ankle-brachial index (ABI) test is performed. The right ABI is 1.45, and the left ABI is 1.10. Which of the following is the most appropriate next step in the diagnostic evaluation of this patient?

  1. Measurement of the toe-brachial indexAnswer
  2. B
    Computed tomography angiography of the lower extremities
  3. C
    Immediate surgical arterial bypass
  4. D
    Initiation of a supervised graded exercise program
  5. E
    Administration of broad-spectrum intravenous antibiotics

Answer

Measurement of the toe-brachial index
The correct answer is measurement of the toe-brachial index (TBI). This patient presents with classic signs of critical limb ischemia (CLI), including ischemic rest pain (pain awakening him at night, relieved by dangling the leg) and a non-healing distal ulcer. The initial diagnostic test for peripheral arterial disease is the ankle-brachial index (ABI). However, in patients with long-standing diabetes mellitus or chronic kidney disease, medial arterial calcification often renders the tibial arteries rigid and non-compressible. This results in a falsely elevated ABI (> 1.30). Because the digital arteries of the toes are typically spared from this calcification process, assessing the toe-brachial index (TBI) is the most appropriate next step to accurately evaluate distal limb perfusion.

Step-by-Step Solution

1
Evaluate the patient's clinical presentation.
The patient has ischemic rest pain (worse at night, relieved by dependency) and a non-healing foot ulcer, which are hallmark signs of Critical Limb Ischemia (CLI).
Identifying the severity of the peripheral arterial disease is necessary to determine the urgency and type of diagnostic workup.
2
Interpret the ankle-brachial index (ABI) results.
The right ABI is 1.45. Normal ABI is 0.91 to 1.30. An ABI > 1.30 is abnormally high.
In patients with long-standing diabetes or end-stage renal disease, medial arterial calcification (Mönckeberg's arteriosclerosis) makes the arteries stiff and non-compressible, leading to falsely elevated, unreliable ABI readings.
3
Select the most appropriate subsequent diagnostic test.
Measurement of the toe-brachial index (TBI) is indicated.
Because digital arteries of the toes are generally spared from medial calcification, a TBI provides a reliable assessment of distal perfusion when the ABI is falsely elevated.

Key Concept

In patients with diabetes mellitus or end-stage renal disease, an ABI > 1.30 indicates non-compressible, calcified vessels; the next appropriate diagnostic step is a toe-brachial index (TBI) or arterial duplex ultrasound.
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Topics

Cardiothoracic and Vascular Surgery

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