A 67-year-old man comes to the emergency department due to worsening left foot pain. The pain involves the entire left foot and is severe in the forefoot. The pain began a day prior while the patient was lying in bed watching television. He immediately sat up and dangled his foot over the side of the bed, but this did not improve the pain as it had during past episodes. Although the pain was initially mild, it progressively worsened over the course of the day. The patient tried heat packs and over-the-counter pain medication, which he takes intermittently for chronic low back pain, without relief. Medical history includes hypertension and hyperlipidemia. The patient smokes 1-2 packs of cigarettes daily. Temperature is 36.7 C (98 F), blood pressure is 146/90 mm Hg, and pulse is 92/min. On examination, the skin of both lower legs is shiny and hairless, and the left foot is mottled and cooler to the touch than the right foot. Pulses are not palpable in either foot but can be detected with doppler in the right foot. The left foot has capillary refill of 4-5 seconds. The patient has difficulty moving his left foot and toes. Which of the following is the most likely cause of the patient's new symptoms?
This patient likely has peripheral artery disease (PAD) given his risk factors (eg, smoking, hypertension, hyperlipidemia), symptoms (eg, rest pain that improved with dangling), and clinical findings (eg, shiny, hairless legs). In patients with PAD, atherosclerosis of peripheral arteries (eg, popliteal artery) may be complicated by plaque disruption. This can lead to thrombosis and acute-on-chronic limb ischemia (eg, mottling, coolness, prolonged capillary refill, paresis).
In contrast to patients without PAD who develop acute limb ischemia (eg, due to arterial embolus from atrial fibrillation) and typically have abrupt onset of the classic 6 Ps of ischemia, those with existing PAD who develop acute-on-chronic limb ischemia (eg, due to thrombosis from plaque disruption) often lack these classic features or develop them more slowly (eg, over 1 day, as in this patient). This is because preexisting collateral circulation, which formed in response to progressive accumulation of atherosclerosis in the primary arterial circulation (eg, popliteal artery), can supply some perfusion to the affected distal limb, as in this patient with prolonged but not absent capillary refill. Even with collateral circulation, distal limb perfusion is still typically inadequate; therefore, most patients with acute-on-chronic limb ischemia require emergency intervention (eg, intravenous heparin infusion, thrombolysis, thrombectomy).
(Choice B) Exaggerated cutaneous vasoreactivity is seen in Raynaud phenomenon and may cause skin color changes. However, vasoconstriction is typically triggered by cold, is more common in the hands, and usually lasts minutes not hours.
(Choice C) Increased fascial compartmental pressure can lead to compartment syndrome, a limb-threatening cause of pain and paresis (a late sign). However, compartment syndrome typically occurs after trauma (eg, crush, fracture) or ischemia-reperfusion and is classically associated with tense swelling and increased pain on passive stretch.
(Choice D) Popliteal vein thrombosis more commonly causes distal warmth and/or swelling (ie, decreased venous outflow) rather than coolness and prolonged capillary refill (ie, decreased arterial inflow).
(Choice E) Thromboangiitis obliterans, a tobacco-associated vasculitis, can lead to extremity ischemia, pain, and discoloration. However, symptoms typically begin distally (eg, digital ischemia) before progressing proximally. In addition, patients are typically age <45 and often have normal distal pulses.
Educational objective:
Due to preexisting collateral circulation, acute limb ischemia in the setting of chronic peripheral artery disease (PAD) often presents less dramatically than in patients without PAD. Emergency intervention is still necessary.