Extensive extraspinal hyperostoses after long-term oral retinoid treatment in a patient with pityriasis rubra pilaris

We describe a patient with severe pityriasis rubra pilaris in whom extensive extraspinal hyperostoses developed after 13 years of oral retinoid treatment. The most prominent abnormality was a bridging exostosis between the left acetabulum and collum. X-ray examinations of the spine during retinoid therapy showed no abnormalities. During oral retinoid treatment, it is important to ask the patient on a regular basis about any skeletal pains or mobility restriction. Normal spinal x-ray results are no guarantee that a patient is free of hyperostoses. Discontinuation of acitretin therapy resulted in a severe exacerbation of the patient's pityriasis rubra pilaris after 2 weeks. The clinical response to administration of azathioprine was clearly inferior to that of acitretin. However, low-dose oral methotrexate therapy appeared to be a good alternative in this patient, with a clinical result comparable to acitretin and no side effects after 6 months of therapy.