A 14‐year‐old girl with Smith‐McCort dysplasia misdiagnosed as seronegative juvenile idiopathic arthritis

Dear Editor, Spondylo-epi-metaphyseal dysplasias (SEMDs) are a heterogeneous group of disorders with differing modes of inheritance, all of which are defined by the combination of vertebral, epiphyseal and metaphyseal abnormalities. The specific diagnosis is based on the specificity of the skeletal manifestations or the presence of characteristic extraskeletal features. Dyggve-Melchior-Clausen syndrome (DMC) and Smith-McCort dysplasia (SMC) are rare autosomal recessive SEMDs. SMC (OMIM: 607326), which is a rare variant of DMC syndrome without evidence of mental retardation, has been shown to be allelic to DMC syndrome. Smith-McCort dysplasia is a progressive, autosomalrecessive SEMD that may be misdiagnosed in clinical practice as juvenile idiopathic arthritis (JIA). The clinical importance of this rare disorder may be attributed to its clinical similarity to JIA, which has a very different prognosis and treatment regimen. Typical dysplastic skeletal abnormalities, which occur mainly in the spine and iliac bones, and the absence of synovial inflammation enable the differential diagnosis of SMC from JIA. We present the case of a 14-year-old girl with SMC who was misdiagnosed as having JIA. A 14-year-old girl was admitted to our hospital with pain in the bilateral hip and leg that had hindered her normal walking for 3 months. Evaluation of the clinical history revealed that the pain had started from both hips and spread to the legs, and had gradually reduced her ability to walk. She reported that she could not stand or walk without support for the previous 2.5 months. The history of the patient revealed no evidence of swelling, redness or warmth of the joints during this time period. Approximately 3.5 months prior to presentation at our hospital with these complaints, she had consulted an orthopedic surgeon, who had recommended bilateral total hip arthroplasty. In the meantime, she was admitted to our hospital and was evaluated at the Departments of Pediatrics and Rheumatology, _Istanbul University Cerrahpasa Medical Faculty, Turkey. After a diagnosis of a seronegative rheumatoid arthritis, treatment was initiated with a regimen of prednisolone 5 mg once daily, methotrexate 15 mg/ week, calcium–vitamin D once daily, and folic acid once daily, twice a week in the Department of Rheumatology. These treatments did not produce any change in her pain or walking ability. The patient is the fifth child in a family in which the parents are non-consanguineous. She had no history of severe disease or disability, apart from slow growth and developmental delay. Neurological examination was normal, and the patient was still receiving primary education. She had short and fusiform hand fingers. Increased anteroposterior chest diameter and kyphoscoliosis were present, and the proximal portions of the upper and lower limbs were short. She had pain and limitation regarding range of motion in the knee and hip joints bilaterally. She also had bilateral valgus deformity of the knee and ankle joint. The right and left leg lengths were 63 and 67 cm, respectively. The patient’s serum 25-hydroxyvitamin D, parathyroid hormone, thyroxine, thyroid stimulating hormone, acute phase response proteins, serum protein electrophoresis, and bone, liver, and kidney profiles were all normal. Urine amino acids were normal and there was no excretion of mucopolysaccharides. Spinal radiography revealed platyspondyly in almost all the vertebral bodies (Fig. 1), and pelvis radiography revealed lacy iliac bones and dysplasia of the acetabulum and femoral heads bilaterally (Fig. 2). In a cervical magnetic resonance imaging, there was odontoid hypoplasia, platyspondyly at multiple levels, irregularities of the end-plates, and characteristic double-humped appearance due to a wedge-shaped ossification defect. The bone mineral density (BMD) of the patient was measured using dual-energy X-ray absorptiometry (DEXA; Hologic QDR-4500, Bedford, International Journal of Rheumatic Diseases 2012; 15: e55–e57