Afebrile Pneumonia in a Patient With Multicentric Castleman Disease on Siltuximab: Infection Without Fever on Anti-Interleukin-6 Therapy

Castleman disease is a lymphoproliferative disorder characterized by atypical lymph node hyperplasia and systemic symptoms; it can also affect the skin and blood counts. The condition is categorized by the extent of involvement (unicentric or multicentric) and the observed lymph node pathology (hyaline-vascular, plasma cell or mixed cellularity). Pathogenesis also has a role in the classification and treatment of multicentric Castleman disease; this variant can either be related to the presence of human herpesvirus-8 (HHV-8) infection or associated with POEMS (polyneuropathy, organomegaly, endocrinopathy, monoclonal proteins and skin changes) syndrome, or idiopathic. The principal cytokine responsible for causing idiopathic multicentric Castleman disease (IMCD) is interleukin-6 (IL-6). Therefore, treatment with agents that bind to IL-6 (such as siltuximab) or block the IL-6 receptor (such as tocilizumab) has been used. We report a woman with IMCD who was successfully being treated with siltuximab; her cutaneous manifestations and systemic disease (lung and lymph nodes) improved within three months. However, nine months after starting siltuximab, she developed a worsening cough and new infiltrates in the right lung on positron emission tomography/computed tomography (PET/CT) scan; there were no other constitutional symptoms such as fever, night sweats or fatigue. Differential diagnosis included Castleman disease recurrence, lung neoplasm and infection. Her pulmonary symptoms and infiltrates on scan resolved after treatment with systemic levofloxacin, indicating that she had an antibiotic-sensitive afebrile pneumonia. We postulate that her siltuximab therapy blocked the IL-6-associated fever and constitutional symptoms that normally are a hallmark of pneumonia. Therefore, patients who are receiving medications such as siltuximab and tocilizumab that block the IL-6 pathway and impair the acute phase inflammatory response may fail to manifest constitutional symptoms such as fever when infected.