Great toe systolic pressure in peripheral vascular disease

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A 68-year-old woman is assessed for a 6-month history of progressive exertional leg discomfort, described as a “heaviness” involving both calves. The symptoms are relieved within 5 to 10 minutes of rest. She has noted the same limiting heaviness with bicycling. Medical history is significant for hypertension, type 2 diabetes mellitus, and hyperlipidemia; she does not smoke cigarettes. Medications are valsartan, hydrochlorothiazide, metformin, and rosuvastatin.

On physical examination, the patient is afebrile. Blood pressure is 130/84 mm Hg in both arms. The highest right foot systolic pressure is 184 mm Hg; the highest left foot systolic pressure is 186 mm Hg. Pulse rate is 78/min and regular, and respiration rate is 14/min. BMI is 30. Distal pulses are diminished but equal bilaterally. Sensation to light touch is diminished bilaterally in the toes extending to the midfoot. No abdominal or femoral bruits are present. Deep tendon reflexes at the knees and ankles are 2+ and symmetric. Strength is 5/5 throughout in the lower extremities.

Which of the following is the most appropriate diagnostic test to evaluate her exertional leg pain?

A: Electromyography and nerve conduction studies
B: Exercise ankle-brachial index
C: Great toe pressure measurement
D: Lumbar MRI

MKSAP Answer and Critique

The correct answer is C: Great toe pressure measurement.

The most appropriate test to perform in this patient is measurement of the great toe pressure. The ankle-brachial index (ABI) is obtained by measuring the systolic pressures in the dorsalis pedis and posterior tibialis arteries on both sides. The ABI for each leg is the highest ankle pressure for that side divided by the highest brachial pressure (regardless of side). An ABI of 0.90 or lower establishes a diagnosis of peripheral arterial disease (PAD). In this patient, the ABI is greater than 1.40 bilaterally. An ABI above 1.40 suggests noncompressible vessels, which may reflect medial calcification but is not diagnostic of flow-limiting atherosclerotic disease. An ABI greater than 1.40 is associated with worse cardiovascular outcomes than a normal ABI. In such cases, an appropriate next step is to either measure great toe pressure or calculate a toe-brachial index (systolic great toe pressure divided by systolic brachial pressure). Vessels within the great toe rarely become noncompressible, and a great toe systolic pressure below 40 mm Hg or a toe-brachial index of less than 0.70 is consistent with PAD.

Although the patient probably has peripheral neuropathy based on the symmetric loss of sensation to light touch, it is unlikely to be related to the patient’s exertional leg pain. Therefore, electromyography and nerve conduction studies would not be helpful at this point.

An ABI obtained immediately following symptom-limited exercise is useful when a high clinical suspicion for PAD remains despite a normal (1.00-1.40) or borderline resting ABI. A decrease of the ABI by 20% compared with the resting ABI is consistent with significant PAD. This patient’s ABI is above the normal range; therefore, exercise ABI would not help to establish the diagnosis.

Although spinal stenosis can produce leg discomfort with walking, patients often describe discomfort with prolonged standing. The discomfort is relieved with lying down or with waist flexion. In this patient, the physical examination does not demonstrate motor or sensory loss that would support nerve root compression as the cause of her symptoms. Additionally, the position adopted for bicycling is less likely to provoke leg pain in patients with spinal stenosis, but can result in claudication due to arterial insufficiency. Lumbar MRI, therefore, is not indicated.

Key Point

In a patient with suspected peripheral arterial disease, an ankle-brachial index above 1.40 is noninterpretable; measurement of the great toe systolic pressure can establish the diagnosis.

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