title: Authors' reply.
authors.affiliation: a Department of Rheumatology , Sint Maartenskliniek , Nijmegen , The Netherlands.
authors.forename: Eam
authors.initials: E
authors.lastname: Mahler
authors.affiliation: a Department of Rheumatology , Sint Maartenskliniek , Nijmegen , The Netherlands.
authors.forename: N
authors.initials: N
authors.lastname: Cuperus
authors.affiliation: b Department of Rheumatology and Clinical Immunology , University Medical Centre Utrecht , Utrecht , The Netherlands.
authors.forename: Jjw
authors.initials: J
authors.lastname: Bijlsma
authors.affiliation: c Department of Orthopaedics , University Medical Centre , Leiden , The Netherlands.
authors.forename: Tpm
authors.initials: T
authors.lastname: Vliet Vlieland
authors.affiliation: a Department of Rheumatology , Sint Maartenskliniek , Nijmegen , The Netherlands.|d Department of Rheumatology , Radboud University Medical Centre , Nijmegen , The Netherlands.
authors.forename: Fhj
authors.initials: F
authors.lastname: van den Hoogen
authors.affiliation: a Department of Rheumatology , Sint Maartenskliniek , Nijmegen , The Netherlands.
authors.forename: A A
authors.initials: AA
authors.lastname: den Broeder
authors.affiliation: a Department of Rheumatology , Sint Maartenskliniek , Nijmegen , The Netherlands.
authors.forename: C H
authors.initials: CH
authors.lastname: van den Ende