New-onset rheumatoid arthritis after anthrax vaccination

Background: Anthrax vaccine was licensed in 1970 and is used to protect individuals exposed to biological warfare and those who may come in contact with Bacillus anthracis in infected animals or in laboratory settings. The current adsorbed anthrax vaccine is regarded as effective and safe. Adverse effects reported include fever, chills, myalgia, arthralgia, and nausea. Four cases of rheumatoid arthritis (RA) temporally related to anthrax vaccine have been reported. As the number of administered doses increases, a better understanding of its adverse events profile will be forthcoming. Objective: To describe another patient with RA temporally related to anthrax vaccination. Methods: A 42-year-old man developed bilateral knee stiffness and pain in all the proximal interphalangeal joints 5 days after receiving the first dose of anthrax vaccine. He reported chills, fever, and joint and neck pain, with a tender nodule at the injection site after dose 2. Hours after receiving dose 3 he experienced fever, chills, nausea, vomiting, and neck, hand, and shoulder pain. The vaccination series was terminated after the third dose. Results: Physical examination revealed moderate swelling and tenderness of his bilateral proximal interphalangeal joints. His complete blood cell count was normal; rheumatoid factor level, 198 IU/mL; erythrocyte sedimentation rate, 53 mm/h; antinuclear antibodies, negative; C-reactive protein level, 2.7 mg/L; and anti-cyclic citrullinated peptide antibody level, 168 EU. Radiographs revealed mild degenerative changes in his hands and knees bilaterally. Conclusions: This case represents a fifth patient with RA temporally related to anthrax vaccine.