An MRI of the lumbar spine is most likely to confirm the diagnosis in this patient. This patient's normal ankle-brachial index (ABI) bilaterally, normal distal pulses, lack of a bruit, normal skin findings, and clinical history all suggest a diagnosis other than peripheral arterial disease (PAD). Patients with pseudoclaudication (lumbar spinal stenosis) may report bilateral leg weakness associated with walking or with prolonged standing; symptoms are aggravated by prolonged standing and are relieved with bending at the waist. Nearly half of patients have absent deep tendon reflexes at the ankles, but reflexes at the knees and muscle strength are usually preserved. The American College of Physicians recommends that advanced imaging with MRI or CT should be reserved for patients with a suspected serious underlying condition or neurologic deficits, or who are candidates for invasive interventions. In the absence of these indications, back imaging is not indicated.
Measuring the exercise ABI can be useful in diagnosing PAD when the resting ABI is normal and the index of suspicion is high for PAD. This patient's history and examination findings point to a diagnosis other than PAD, so measuring the exercise ABI will not add helpful information at this time.
Segmental limb plethysmography is useful in patients with an established diagnosis of PAD to help localize the site of stenosis. In this test, blood pressures are recorded using plethysmographic cuffs placed at the upper thigh, lower thigh, calf, and ankle. A drop in systolic pressure of 20 mm Hg identifies a zone of significant disease.
An ABI greater than 1.40 is associated with calcification of the arterial wall and may occur in patients with medial calcinosis, diabetes mellitus, or end-stage kidney disease. This finding is uninterpretable and is associated with worse cardiovascular outcomes than a normal ABI; therefore, an appropriate next step after this finding is to either measure great toe pressure or calculate a toe-brachial index (systolic great toe pressure divided by systolic brachial pressure), a test that is typically performed in a vascular laboratory. This patient's ABI is normal, so measurement of the toe-brachial index is not necessary.