Progressive pseudorheumatoid dysplasia: a masquerader of juvenile idiopathic arthritis

A 10-year-old male firstborn child of a nonconsanguineous marriage is symptomatic since six years with difficulty in walking, morning stiffness gradually progressive swelling and pain in multiple joints.
Normal developmental milestones and no family history.
Wt- 22.5kg, ht-120cms (<3rdpercentile)[1].
Serum calcium, thyroid, CRP, RA, and HLA-B27 levels were all negative

1) X-ray pelvis with both hips shows, irregular and enlarged epiphyses of the head of femur and greater trochanter of femur with narrowing of the hip joint space with early changes of osteoarthritis of bilateral femoro-acetabular joints.

2) Frontal and lateral radiograph of the dorsolumbar spine shows platyspondyly with anterior beaking of the vertebral bodies.

3) Frontal X-ray of both hands shows enlarged phalangeal epiphyses and metaphyses with early osteoarthritic changes in the interphalangeal joints. There is mild periarticular osteopenia.

4) X-Ray bilateral Knee and right elbow shows epiphyseal enlargement and irregularity in distal aspect of humerus, proximal ends of radius and ulna and proximal part of tibia.

Progressive pseudorheumatoid dysplasia (PPRD) also called spondyloepiphyseal dysplasia tarda with progressive arthropathy (SEDT-PA) is a rare (approximately 1 to 9 per million in the UK [Wynne-Davies et al 1982]. However, it is more common in Turkey and Middle East whose exact prevalence is unknown [2,6]) hereditary disorder with autosomal recessive inheritance. There is slight male predominance pattern noted [3,4].

Presenting from age 3 to 8 with abnormal gait and arthralgia with seronegative progressive osteoarthritis primarily affecting the articular cartilage [5,6]. This ultimately results in fixed flexion deformity of the affected joints. Classic imaging findings in  PPRD  include  kyphoscoliosis and platyspondyly with anterior beaking of vertebrae, coxa vara deformity , enlargement and irregularity of epiphyses of the small and large joints and early osteoarthritic changes in the large weight bearing joints (eg hip joint) [8].This leads to secondary disproportionate dwarfism(since the trunk is shorter due to secondary kyphoscoliosis) .Camptodactyly is always seen in adults.[9]Shoulder joints are typically not that severely affected [Dalal et al 2012].

Since joint involvement in SEDT-PA may be confused with juvenile idiopathic arthritis (JIA)[5]. The differentiation between JIA and SEDT-PA is tricky and most cases are misdiagnosed initially as JIA. However, the absence of laboratory changes indicating systemic or synovial inflammation,no joint erosions and the presence of characteristic X-ray changes of spondyloepiphyseal dysplasia (platyspondyly predominantly) help in the differential diagnosis of SEDT-PA from JIA.

The major reason for misdiagnosis is onset in childhood with swelling and arthritic features in peripheral and axial joints.

Although radiologic examination has high accuracy in the diagnosis of PPD, the definitive diagnosis is confirmed with presence of biallelic pathogenic variants in WISP3 on molecular genetic testing [7,10].

Treatment is mainly palliative. Early Physiotherapy may help to preserve joint mobility and joint immobilization should be discouraged. Total replacement arthroplasty of the hips for secondary degenerative changes may become necessary at a very early age . Genetic studies can  be advised for family counseling [8].

Written informed consent was obtained from the patients’ father for the publication and use of images and investigation results in the present case report