A case of urticarial vasculitis in a female patient with lupus: Mycoplasma pneumoniae infection or lupus reactivation?

A 17-year-old female patient affected by systemic lupus erythematosus (SLE) (who had been taking 300 mg/die of hydroxychloroquine for 3 years), Graves' disease (treated with 10 mg/die of tapazole), and celiac disease came to our attention for urticarial vasculitis. She had been taking prednisone (25 mg/die) for 3 days, and her blood tests showed high levels of Mycoplasma pneumoniae IgM and IgG antibodies. The association between urticaria and M. pneumoniae infections can be present in up to 7% of the cases and, to the best of our knowledge, only two reports of urticarial vasculitis and M. pneumoniae in adults are available in the literature. Urticarial vasculitis can also be a rare cutaneous manifestation of SLE (affecting 2% of the patients), and our case is the first in the literature describing the coexistence of M. pneumoniae infection, SLE, and urticarial vasculitis in a pediatric patient, a case that rises an important differential diagnosis issue about the origin of urticarial vasculitis: SLE reactivation or urticarial vasculitis due to M. pneumoniae infection?