Imaging may reveal injuries in intravenous drug users

Parenteral drug abuse is relatively uncommon in Singapore compared with other forms of substance abuse.1 The recent trend, however, of addicts injecting self-dissolve tablets with other drugs, bringing risk of serious limb morbidity, is causing concern.

One such drug that has been linked to this practice is buprenorphine hydrochloride. This agent, better known as Subutex, has U.S. Food and Drug Administration approval and was originally introduced to treat opioid dependence.2 Buprenorphine is also a Schedule III narcotic under the Controlled Substances Act. Subutex is sold as uncoated oval white tablets that are intended for sublingual administration. Each tablet also contains lactose, mannitol, cornstarch, povidone K30, citric acid, sodium citrate, and magnesium stearate.3 Buprenorphine is a partial agonist at the micro-opioid receptor and an antagonist at the k-opioid receptor.

The action of buprenorphine on opioid receptors, and their ability to produce euphoria and opioid-like effects, creates the potential for this drug to be abused.4 Intravenous drug users are known to crush the tablets and attempt to dissolve the powder before injecting the mixture.5 This practice is becoming more common in Singapore.4-6 The reported abuse rate of buprenorphine in France and Australia ranges from 37% to 57%.7,8

Complications related to this practice are well documented.9 Intravenous drug users aim for the "black blood" (vein) and not the "pinkie" (artery) when injecting.10 Peripheral veins become "used," or sclerosed, after a while. Chronic intravenous drug users then resort to injecting in the groin for access into the femoral vein or above the elbow for brachial vein access.

Addicts may inadvertently inject drugs intra-arterially, due to the close proximity of arteries to veins (e.g., brachial and femoral arteries). Intra-arterial injection can also be deliberate. Either way, the practice may lead to distal embolic occlusion, pseudoaneurysm formation, or retained broken needle tips. Management of these limb-threatening arterial injuries can be problematic because this patient group often has significant comorbidities.11

Imaging can play an important role in identifying complications associated with intra-arterial injection. Diagnoses can be made using plain-film x-ray, ultrasound, CT, and digital subtraction angiography.

DISTAL EMBOLIC OCCLUSION

Arterial embolic occlusions most likely occur when drugs are not dissolved completely before injection. Incompletely dissolved constituents may then contribute to thrombus formation.4 Occlusion occurs at the distal branches, which is more in keeping with embolic phenomenon than direct vessel injury. Other possible etiologies for distal artery occlusion include chemical endothelial injury and vasospasm.12

The severity of limb ischemia at presentation depends on several factors. These include symptomatic duration, site of occlusion, and severity of occlusion. We found that patients with slow or delayed flow on DSA had better clinical outcomes than patients with no blood flow in arteries distal to the injection site. Patients with higher levels of occlusion in the forearm and leg arteries, and delayed presentation to the hospital, have worse outcomes that often result in amputation.13

Our experience shows DSA to be an excellent modality for detecting arterial occlusions in this patient group. It provides a dynamic visualization of blood flow and a clear demonstration of occlusion points, which often occur in the tiny digital vessels (Figures 1 and 2). Collateral flow, incomplete stenoses with poor flow, and vasospasm may be seen as well. The same changes may not be detected as reliably on CT or MR angiography. DSA may also help when planning interventional procedures to treat occlusions.

The vessel in question should preferably be imaged proximal to the injection site. This may help demonstrate any coexisting pseudoaneurysms and/or arteriovenous fistula formation. Larger trials and greater experience with this patient group is required to evaluate the value of angiography in predicting the need for early surgical intervention and the efficacy of thrombolysis in the acute setting. Optimal management may remain difficult, however. This group of patients is unlikely to provide a reliable history of drug use, symptomatic onset, and duration of symptoms. They also may not comply with the recommended treatment strategy.

Pseudoaneurysms can form as a result of direct injury to the vessel wall or secondary to local infection adjacent to an artery that causes arterial wall breakdown. Rupture of the pseudoaneurysm is a serious complication that can lead to the loss of the limb or to death by exsanguination.14 It is important to distinguish a pseudoaneurysm from an abscess. Inappropriate incision and drainage could lead to catastrophic blood loss. The overall amputation rate may reach up to 33% in patients with pseudoaneurysms.15

Most femoral pseudoaneurysms less than 3 cm in diameter will spontaneously thrombose. This may be observed with serial ultrasound examinations in symptomatic patients. Open repair is usually undertaken when there is associated soft-tissue infection/collection and/or rapid expansion of the pseudoaneurysm observed over a period of time.16

All patients we have treated for pseudoaneuryms so far have been asymptomatic, with involvement of the femoral artery. Both CT and DSA were useful in delineating the pseudoaneurysm's arterial supply and its relationship with the surrounding vascular structures (Figures 3-5).

RETAINED NEEDLE TIPS

Intravenous drug users are at risk of retained needle fragments. Chronic drug users reuse needles for multiple injections, which makes the needles prone to fracture. Addicts also inject into areas of scar tissue and sometimes bend needles to inject in difficult-to-access central areas when peripheral sites are no longer available. This practice again may fracture the needle. Retained needles and needle fragments represent a potential hazard for the patient and attending healthcare workers, even more so if the patient has HIV or hepatitis B. The needles may also migrate within tissues and embolize vessels.

Smaller needle fragments may not always be seen easily on plain-film x-rays, even though they are metallic and hence radiopaque. CT not only helps detect needle fragments, but it also provides important anatomic information prior to surgery (Figures 5 and 6). Retained needle fragments can be a source of infection and result in local abscess formation. Surgical removal of the needle fragment is the treatment of choice.

In summary, the trend of injecting self-dissolved drug preparations may lead to serious limb morbidity. A high index of suspicion is warranted when patients present with unusual arterial complications that may be inconsistent with their clinical history. Radiologists should be familiar with the various arterial complications of self-injection and the role of imaging in their detection.

DR.TAN is a resident and DR. VENKATESH is an assistant professor and consultant radiologist in the department of diagnostic radiology at National University Hospital, Yong Loo Lin School of Medicine, National University of Singapore.

Acknowledgement

This article is adapted from Tan CH, Venkatesh SK, Lim A, Tsai L. Arterial complications of self-prepared drug injections: imaging a recent trend. Educational exhibit presented at the annual meeting of the Radiological Society of North America, Chicago; November 2006:971.

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