The laboratory findings revealed that the levels of serum IgG, IgA, IgM, and CRP in the PC‐iMCD patients were significantly higher than those in the IgG4‐RD patients (p = 0.013, p < 0.001, p < 0.001, and p < 0.001, respectively). The gene discussed is CD40LG; the disease is pachyonychia congenita.