Retroperitoneal Fibrosis: An Extraarticular Manifestation of Ankylosing Spondylitis CLAIRE M. A. LEBLANC, 1 ROBERT D. INMAN, 2 PETER DENT, 3 CHARLES SMITH, 1 PAUL BABYN, 1 AND RONALD M. LAXER 1 Introduction Idiopathic retroperitoneal fibrosis (RPF) was first de- scribed as a clinical entity in 1948 (1). Most patients with RPF are 30 – 60 years old, and very few pediatric cases have been reported. Although in most cases the RPF is idiopathic, it may also be secondary to underlying infec- tion, malignancy, drugs, radiation, trauma, or surgery. In most patients, fibrosis is confined to the retroperitoneal region of the lower lumbar spine; however 15% have fi- brosis in other organs (2). Spondylarthritis, which may also be complicated by extraarticular fibrosis, has been reported in patients with RPF. We present a case of a 7-year-old boy who originally presented with RPF and was later diagnosed as having spondylarthritis, and discuss the relevance of this association. Case report A 19-month-old boy presented with a 6-week history of severe nocturnal leg pain, reduced ambulation, and morn- ing stiffness of 2 hours duration. On examination, there was limited flexion, stress pain of both hips, and tight tendo Achillis, but joint effusions were not detected. Lab- oratory tests showed hemoglobin (Hgb) 97 gm/dl, Wester- gren erythrocyte sedimentation rate (ESR) 29 mm/hour, and negative antinuclear antibody (ANA) and rheumatoid factor (RF). Chest, abdominal, and hip radiographs and abdominal ultrasound were normal. The patient was treated with 70 mg/kg/day of aspirin for possible juvenile rheumatoid arthritis, which only improved the stiffness. At 5 years of age, he developed worsening hip pain and stiffness. Examination showed hip and knee flexion con- tractures, reduced back flexion, and warm, non-tender an- kles, but no effused joints. The Hgb was 85 gm/dl, platelet count 613,000/mm 3 , and ESR 42 mm/hour. The results of iron studies, albumin, creatinine kinase, urinalysis, and HLA–B27 were either normal or negative. Radiographs of the lumbosacral spine, sacroiliac joints, and hips were reported as normal. Treatment consisted of an injection of triamcinolone hexacetonide in both hips that initiated a dramatic, but short-lived improvement. Subsequently, naproxen (18 mg/kg/day) and oral prednisone (0.6 mg/kg every other day) were initiated. Two years later the boy developed lower abdominal pain, nausea, vomiting, and anorexia. Hip pain and stiff- ness recurred despite treatment with prednisone 0.25 mg/kg every 48 hours. Examination revealed a distended abdomen and palpable left kidney. Laboratory evaluation revealed the following findings: Hgb 91 gm/dl (normal 120 –160), ESR 45 mm/hour (normal 1–10), urea 7.6 mmol/ liter (normal 2.9 –7.1), creatinine 94 mol/liter (normal 10 – 80), and normal urinalysis. Abdominal ultrasound and intravenous pyelogram showed severe bilateral hydrone- phrosis, with minimal vesicoureteral reflux on voiding cystourethrogram. Extensive fibrotic tissue extending from the pelvic brim to the lower pole of kidneys was seen on abdominal computerized tomography (CT) and at laparot- omy (Figure 1A). Subsequently, a right ureterolysis with omental wrap and left ureter bypass surgery using the Boari flap procedure were performed. Microscopic exam- ination revealed dense collagenized fibrosis with chronic inflammatory cells, compatible with retroperitoneal fibro- sis (Figure 1B). At 8 years of age the patient developed low back pain and stiffness. Marked hip and knee flexion contractures, and reduced hip and back range of motion were noted, as well as bilaterally tight tendo Achillis requiring heel cord and plantar fascia releases. The neurologic examination was normal. Abdominal CT showed improvement of hy- dronephrosis and resolution of RPF; the hips appeared normal. Magnetic resonance imaging (MRI) of the spine and spinal cord was normal. Treatment with oral pred- nisone (15 mg/day) was required to control symptoms and 1 Claire M. A. LeBlanc, MD, FRCPC, Charles Smith, MD, FRCPC, Paul Babyn, MD, FRCPC, Ronald M. Laxer, MD, FRCPC: University of Toronto, and The Hospital for Sick Children, Toronto, Ontario, Canada; 2 Robert D. Inman, MD, FRCPC: University Health Network, University of Toronto, Ontario, Canada; 3 Peter Dent, MD, FRCPC: McMaster Uni- versity Medical Centre, Hamilton, Ontario, Canada. Address correspondence to Claire M. A. LeBlanc, MD, FRCPC, Division of Rheumatology, Room 8253 Elm Wing, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario M5G 1X8, Canada. E-mail: claire.leblanc@ sickkids.on.ca. Submitted for publication March 18, 2001; accepted in revised form October 24, 2001. Arthritis & Rheumatism (Arthritis Care & Research) Vol. 47, No. 2, April 15, 2002, pp 210 –214 DOI 10.1002/art1.10267 © 2002, American College of Rheumatology CASE REPORT 210