[Orphan diseases in rheumatology. Exemplified by polyarteritis nodosa].

The term orphan disease is used for those diseases which are diagnosed in less than 5 out of 10,000 persons. An example of an orphan disease in rheumatology is panarteritis nodosa (PAN), the clinical manifestation of which ranges from mild forms to life-threatening situations. The scientific publications on the diagnosis and therapy of PAN are usually limited to casuistics and small case studies. Treatment of this disease is usually carried out analogue to other forms of vasculitis but the therapeutics used are not formally approved for PAN. With this in mind it is much more realistic to treat such patients in specialized centers or at least to allow an evidence-based medical treatment in, for example network associations, using the targeted documentation of patients.