Rhabdomyolysis Occurring After Use of Cocaine Contaminated With Fentanyl Causing Bilateral Brachial Plexopathy

Discussion

Rhabdomyolysis is a condition defined by myocyte necrosis that results in release of cellular contents and local edema. Inciting events may be traumatic, metabolic, ischemic, or substance induced. Common substances indicated include cocaine, amphetamines, acetaminophen, opioids, and alcohol.¹⁰ It classically presents with muscle pain and a marked elevation in serum CPK level, but other metabolic disturbances, acute kidney injury, or toxic hepatitis may also occur. A more uncommon sequela of rhabdomyolysis is plexopathy caused by edematous swelling and compression of the surrounding structures.

Rare cases of brachial plexopathy caused by rhabdomyolysis following substance use have been described. In many of these cases, rhabdomyolysis occurred after alcohol use with or without concurrent use of prescription opioids or heroin.^7-9 One case following use of 3,4-methylenedioxy-N-methylamptamine (MDMA) and marijuana use was reported.¹ Another case of concurrent brachial plexopathy and Horner syndrome in a 29-year-old male patient following ingestion of alcohol and opioids has also been described.⁵ The rate of occurrence of this phenomenon in the general population is unknown.

In the case of our patient, cocaine metabolite and fentanyl were the only substances found on urine drug screen. The patient had used crack cocaine that had presumably been contaminated with fentanyl, a high potency synthetic opioid. The rate of fentanyl contamination of street drugs is variable. It is a subject of high concern, considering the increasing rates of synthetic opioid overdose-related deaths. According to the US Centers for Disease Control and Prevention, synthetic opioids have played a role in the increasing rates of cocaine-related overdose deaths. Conversely, in more than half of all overdose deaths involving fentanyl derivatives, patients also tested positive for cocaine, methamphetamine, or heroin. In recent studies conducted in various cities in the northeastern US, rates of fentanyl metabolite detection were much higher than rates of reported fentanyl use.¹¹ Cases of crack cocaine contamination with fentanyl derivatives have been reported in Canada and Washington.¹²

The pathophysiology of rhabdomyolysis caused by substance use has not been definitively identified, but it is hypothesized that the cause is 2-fold. The first insult is the direct toxicity of the substances to myocytes.^8,9 The second factor is prolonged immobilization in a position that compresses the affected musculature and blood supply, causing both mechanical stress and ischemia to the muscles and brachial plexus. This prolonged immobilization can frequently follow use of substances, such as alcohol or opioids.⁹ Cases have been reported wherein rhabdomyolysis causing brachial plexopathy occurred despite relatively normal positioning of the arms and shoulders during sleep.⁹ In our case, the patient had fallen asleep with his arms crossed over his chest in the prone position with his head turned, though he could not recall to which side. Although he stated that he had slept in this position regularly, the effects of fentanyl may have prevented the patient from waking to adjust his posture. This position had potential to compress the musculature of the neck and shoulders and restrict blood flow, resulting in the focal rhabdomyolysis seen in this patient. In theory, the position could also cause a stretch injury of the brachial plexus, although a pure stretch injury would more likely present unilaterally and without evidence of rhabdomyolysis.

Chronic ethanol use may have been a major contributor by both sensitizing the muscles to toxicity of other substances and induction of CYP450 enzymes that are normally responsible for metabolizing other drugs.⁸ Alcohol also inhibits gluconeogenesis and leads to hyperpolarization of myocytes, further contributing to their susceptibility to damage.⁹ Our patient had a prior history of alcohol use years before this event, but not at the time of this event.

Our patient had other known risk factors for rhabdomyolysis, including his long-term statin therapy, but it is unclear whether these were contributing factors in his case.¹⁰ Of the medications that are known to cause rhabdomyolysis, statins are among the most commonly described, although the mechanism through which this process occurs is not clear. A case of rhabdomyolysis following use of cocaine and heroin in a patient on long-standing statin therapy has been described.¹³ Our review of the literature found no cases of statin-induced rhabdomyolysis associated with brachial plexopathy. It is possible that concurrent statin therapy has an additive effect to other substances in inducing rhabdomyolysis.

Parsonage-Turner syndrome, also known as neuralgic amyotrophy, should also be included in the differential diagnosis. While there have been multiple etiologies proposed for Parsonage-Turner syndrome, it is generally thought to begin as a primary inflammatory process targeting the brachial plexus. One case report describes Parsonage-Turner syndrome progressing to secondary rhabdomyolysis.⁶ In this case, no primary etiology was identified, so the Parsonage-Turner syndrome diagnosis was made with secondary rhabdomyolysis.⁶ We believe it is possible that this case and others may have been misdiagnosed as Parsonage-Turner syndrome.