Sternoclavicular Joint Septic Arthritis and Anterior Mediastinal Mass in a Young Athlete: Possible Immune-modulatory Effect of Growth Hormone.

Septic arthritis of sternoclavicular joint (SCJ) is a rare disease, however, not uncommon in patients who abuse intravenous drugs. It can present with a wide range of manifestations that can pose diagnostic challenges, which can result in a delay in diagnosis and treatment. Over the last few decades, there is a surge in the use of nonprescription recombinant human growth hormone (rhGH) by the young healthy population and athletes for its purported ergogenic effects. Furthermore, we lack quantitative information about the adverse effects of the chronic use of rhGH in a healthy population due to the scarcity of epidemiological data. We are reporting a case of a young male athlete who was chronically using the subcutaneous rhGH formulation to build lean body mass, and presented with septic arthritis of right SCJ due to methicillin-sensitive Staphylococcus aureus (MSSA) complicated by a necrotic inflammatory response involving the mediastinum which infiltrated the apical lung parenchyma. The clinical presentation masqueraded as the mediastinal mass raising the suspicion of mediastinal malignancy. Histological analysis of the tissue of SCJ and mediastinal area revealed no malignant cells but a lymphocyte-predominant inflammatory response with germinal centers was observed, which was an atypical response to MSSA bacterial infection. We have reviewed the literature to elucidate the immune-modulatory effect of rhGH, as the chronic use of rhGH by our patient probably has contributed to an atypical immune response to MSSA. The patient was treated with an extended duration of parenteral antibiotics and multiple incision and debridements to achieve complete resolution of infection over the next six months. This is a unique case of septic arthritis of right SCJ in a patient on chronic subcutaneous rhGH which masqueraded as a mediastinal mass raising concern of malignancy; moreover, it highlights the probable immune-modulatory role of rhGH which instigated an atypical immune response to MSSA infection.