We present the case of a patient with long-standing history of ankylosing spondylitis without an established diagnosis; highly elevated rheumatoid factors; osteoarthritis of both ankles; newly diagnosed granulomatosis with polyangiitis (GPA) with pulmonary changes; severe progressive acute polyneuropathy of the upper and lower extremities. The patient received treatment with intravenous methylprednisolone 1 mg/kg daily for 15 days with gradual dose reduction to 8 mg daily, pulse therapy with intravenous methylprednisolone 1 g and intravenous cyclophosphamide 1 g monthly for 5 months, after that rituximab 600 mg intravenous in day 1,8, 16, 23, symptomatic treatment with B vitamins. Patient responded well to treatment and gradual restoration of mobility of the lower extremities, reduction of numbness in hands and feet, and complete resolution of ankle osteoarthritis was observed. Some polymorphisms appear to confer risk to multiple autoimmune diseases. Studies of familial associations between GPA and other autoimmune diseases have concluded that first-degree relatives of persons with GPA have a modest increase in risk of common autoimmune diseases in general (relative risk 1.32) and of rheumatoid arthritis, multiple sclerosis, psoriatic arthritis in particular.