Erythema Induratum (Nodular Vasculitis) of the Lower Extremities Without Tuberculosis in Psoriasis on Secukinumab (Interleukin 17A Inhibition): A Case Report

Erythema induratum/nodular vasculitis (EI/NV) classically associates with tuberculosis (TB), yet TB-negative disease is increasingly recognized in low-prevalence settings. A 58-year-old nurse with palmoplantar psoriasis controlled on secukinumab developed 6-8 months of exquisitely tender, ulcerating lower-leg nodules refractory to multiple antibiotics. Cultures were largely unrevealing; TB testing and broad microbial cell-free DNA were negative. Incisional biopsies showed lobular panniculitis with mixed inflammation and focal vasculitis, consistent with EI/NV; special stains/PCR for mycobacteria were negative. Multidisciplinary management included brief targeted Gram-positive coverage, high-dose prednisone taper, temporary cessation of IL-17 blockade, and transition to colchicine for steroid-sparing control. Within weeks, no new lesions appeared, and prior ulcers healed. This case underscores the importance of clinicopathologic correlation, rigorous infectious exclusion, and coordinated dermatology - infectious diseases - rheumatology care, favoring individualized anti-inflammatory therapy over empiric antituberculous treatment when TB risk is low and diagnostics are negative.