This patient has sternoclavicular joint septic arthritis. Although there is an increased incidence of Pseudomonas aeruginosa infection in IV drug users, S. aureus is still the most common organism. Ross et al states "Staphylococcus aureus is now the major cause of sternoclavicular septic arthritis in intravenous drug users. Pseudomonas aeruginosa infection in injection drug users declined dramatically with the end of an epidemic of pentazocine abuse in the 1980s." The referenced article by Goldin et al is from the New England Journal of Medicine reports that all of their cases of SC joint septic arthritis were in intravenous drug abusers and that P. aeruginosa grew out of 3 patients and S. aureus grew out of 1 patient. A more recent article by Abu Arab et al reported that Staph aureus was most common even in IV drug users. The review article by Higginbotham and Kuhn note that risk factors for SC joint septic arthritis include hemodialysis, immunocompromise, alcoholism, and HIV. Neisseria gonorrhoeae, fungal, and candida present in HIV patients.
Treatment is I&D and appropriate antibiotics, although aspiration and abx have shown some success too. CT and MRI are useful in diagnosis, and open biopsy or aspiration is recommended for definitive diagnosis.
Higginbotham TO, Kuhn JE: Atraumatic disorders of the sternoclavicular joint. J Am Acad Orthop Surg 2004;13:138-145.
PMID:15850371 (Link to Abstract)
Goldin RH, Chow AW, Edwards JE Jr, et al: Sternoclavicular septic arthritis in heroin users. N Engl J Med 1973;289:616-618.
PMID:4198821 (Link to Abstract)
Abu Arab W, Khadragui I, Echavé V, Deshaies A, Sirois C, Sirois M. Surgical management of sternoclavicular joint infection. Eur J Cardiothorac Surg. 2011 Sep;40(3):630-4.
PMID:21367613 (Link to Abstract)
Ross JJ, Shamsuddin H. Sternoclavicular septic arthritis: review of 180 cases. Medicine (Baltimore). 2004 May;83(3):139-48. Review.
PMID:15118542 (Link to Abstract)