This patient, who presents with fixed, palpable lymphadenopathy in multiple sites and systemic B symptoms (night sweats, fever, and weight loss), most likely has non-Hodgkin lymphoma (NHL) associated with immunosuppression due to the long-term administration of infliximab. Viral infections including Epstein-Barr virus, HIV, human T-cell lymphotrophic virus type-1, and hepatitis B and C viruses are all capable of directly driving transformation of lymphoid tissue to lymphoma or contributing indirectly by causing immunodeficiency, a risk factor for lymphoma development. Specific examples include the development of posttransplant lymphoproliferative disorders presenting as high-grade B-cell NHL caused by ongoing immunosuppression with agents such as cyclosporine or tacrolimus to prevent rejection in solid organ transplantation or graft-versus-host disease in allogeneic hematopoietic stem cell transplantation. Excisional biopsy of an adequate tissue sample that preserves the architecture of the lymph node is required for the diagnosis of lymphoma.

Sarcoidosis can present with or without symptoms that include fatigue, weight loss, joint pain, cough, and shortness of breath. Sarcoidosis is believed to be a consequence of an immune reaction to an unknown antigen, and not immunosuppression.

Testicular cancer can occur late in life but usually does not present with fever and night sweats and would not likely be associated with axillary and cervical lymphadenopathy without mediastinal lymphadenopathy.

Tuberculosis occurs more commonly in patients treated with infliximab. A nonreactive tuberculin skin test cannot be used to exclude tuberculosis because of this patient's immunosuppressed state. However, his extensive extra-abdominal lymphadenopathy without mediastinal lymphadenopathy makes tuberculosis unlikely.