A 30-year-old woman presented to the emergency department with isolated right shoulder pain. The pain started gradually two to three days before. She denied any history of trauma or pain to her shoulder. She appeared in pain, and was seated with her shoulder adducted and internally rotated. Focused exam of her shoulder demonstrated tenderness at the acromioclavicular joint. No swelling, redness, or warmth was appreciated. She was unable to actively or passively abduct her arm because of pain.
A shoulder x-ray did not demonstrate any acute pathology. The patient revealed that she regularly used heroin, and had last used that morning. Track marks were noted on her feet. Labs were ordered to evaluate for inflammation or infection. Labs were notable for a WBC of 9.8, ESR of 28, and CRP of 70.1. An MRI was ordered given the elevation in labs, history of being an intravenous drug user (IVDU), and severe nontraumatic joint pain.
MRI showed marrow edema and enhancement at the acromial process of the scapula suspicious for osteomyelitis and fluid within the subacromial bursa. She left the ED against medical advice, but went to a different hospital with worsening infection and blood cultures positive for Streptococcus mitis. Her history as an IVDU made her ineligible for a PICC line or home health, and she required a six-week hospitalization with IV antibiotics.
Find the diagnosis and case discussion on p. 10.
Diagnosis: Acromioclavicular Joint Septic Arthritis
Skin and soft tissue infectious at injection sites are a common complication of intravenous drug use. Injury and disease related to injections also include infections of other sites, including joints. A systematic review of bone and joint infections in intravenous drug users found a one to two percent self-reported prevalence of septic arthritis and a 0.5 percent prevalence of osteomyelitis. (Drug Alcohol Depend 2017;171:39.) Intravenous drug use, joint surgery, systemic infection, and alcoholism are risk factors for joint infections, which can also arise spontaneously. (Am J Emerg Med 2016;34:934.e5.)
Osteoarticular infections can occur through the parenteral transmission of pathogens inoculated through intravenous drug use. The shoulder and ankle joints are affected in 17.5 percent of cases of septic arthritis in intravenous drug abusers. (Clin Ter 2017;168:e8.) Other commonly infected joints include sternocostal, sternoclavicular, sacroiliac, pubic symphysis, hip, and knee.
Acromioclavicular joint septic arthritis is rare. A literature review found that only 15 cases have been described to date, although it is suspected to be underdiagnosed. (Reumatol Clin 2014;10:37.) Early diagnosis can be made with ultrasound and MRI, while x-rays can show late changes such as erosions. Ultrasound can also be used to guide arthrocentesis, and is the diagnostic test of choice. Treatment includes antibiotic therapy, initially intravenous, with duration of therapy of at least four weeks. Cases that do not respond to medical therapy may require joint lavage or surgical drainage.
It is important for EPs to keep a higher index of suspicion for septic arthritis and osteomyelitis when encountering patients with a history of IVDU and nontraumatic joint pain and to ask patients about IV drug use.
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