Pulmonary thrombosis/PE in 17% of sickle cell pts w/ acute chest syndrome (AJRCCM)

Acute chest syndrome is a dreaded, dangerous complication of sickle cell disease. Its pathophysiology is complex and poorly understood, but can include high pulmonary artery pressures and vasoconstriction of pulmonary arteries. Although microvascular occlusion by abnormal and viscous sickling blood occurs in the systemic circulation, it’s never been shown to occur in the lungs. Dessap et al therefore ask, could undiagnosed pulmonary embolism / pulmonary thrombosis be a heretofore unrecognized contributor to acute chest syndrome?

They performed CT-angiography on 103 consecutive patients who presented to a single hospital in Creteil, France with a diagnosis of sickle cell disease and acute chest syndrome. There were 121 total episodes of acute chest (some had repeated episodes). All the patients had a new area of opacity on chest film, along with dyspnea or chest pain.

RESULTS:

• 17% of patients had a positive CT-angiogram for “pulmonary thrombosis” (radiologically indistinguishable from pulmonary embolism as best as I can tell, but I think they use “thrombosis” to communicate they believe these occurred in situ, not as emboli from deep venous thromboses, for example).
• Most were partial filling defects in large or segmental pulmonary arteries. Only 15% were subsegmental, and these were only “counted” if they were in multiple subsegmental branches.
• All patients with pulmonary thrombosis were screened with leg ultrasound for DVT, and all were negative.

Those with thromboses were treated with at least 6 months of anticoagulation, and in 2 patients who did not / could not take warfarin, pulmonary thrombosis recurred within months with repeated episodes of acute chest syndrome.

My only quibble, question, inquiry here is … what if these thromboses were incidental and unrelated to the acute chest episodes? Do we know the baseline rate of “pulmonary thrombosis” in sickle cell disease patients who are asymptomatic / not experiencing acute chest syndrome? That’s not mentioned here, but a “5% to 56%” rate of pulmonary artery thrombosis has been reported at autopsy of sickle cell disease patients. Is it possible that asymptomatic pulmonary thromboses are common in these patients? Or occur asymptomatically with elevated frequency in patients predisposed to experience acute chest syndrome, but not necessarily causative of or contributory to acute chest? Just a thought, and pretty academic at that, since you’re going to anticoagulate them if you find a clot, right.

Interestingly, 95% of those who were tested for D-dimers (about half) had a positive D-dimer test. Not too helpful in this clinical setting.

Dessap AM et al.  Pulmonary Artery Thrombosis during Acute Chest Syndrome in Sickle Cell Disease. Am J Respir Crit Care Med 2011;184:1022-1029.