EP12 Bilateral lipoma arborescens as a presenting feature of ankylosing spondylitis
Authors: Khalid Sameena , Cox Miriam , Kazmi Muhammad 
Published: April 2020

Abstract

Background
Lipoma arborescens (LA) is a rare, slow growing lesion defined as a villous lipomatous proliferation of the synovial membrane with replacement of the synovial tissue by mature fatty cells. It usually involves the knee and can be associated with degenerative joint disease, trauma, diabetes mellitus and very occasionally with inflammatory arthritis. Diagnosis is made using MRI which shows a synovial mass that is isointense relative to fat and joint effusion. Histologically there is diffuse replacement of the subsynovial layer with mature adipocytes and infiltration of mononuclear cells. Treatment is with synovectomy and treating any underlying condition.

Methods
We present the first case bilateral knee LA as a presenting feature of ankylosing spondylitis.

Results
A 29-year-old Caucasian male presented to a knee orthopaedic surgeon with a two-year history of atraumatic bilateral knee swelling. He had a ten-year history of intermittent knee pain and stiffness which was unresponsive to non-steroidal anti-inflammatory drugs (NSAIDs) and physiotherapy. Examination revealed large bilateral knee effusions with restriction of movement. Plain radiographs of his knee joints showed minor osteophytic lipping laterally on his right knee. He had an MRI of both his knees which showed bilateral joint effusions and bilateral LA. He was referred to the rheumatology team for consideration of underlying inflammatory arthritis. Further questioning revealed no history of uveitis, dactylitis, psoriasis, inflammatory bowel disease but lower back pain which was long standing. Blood tests showed rheumatoid factor, anti-CCP, anti-DsDNA, ENA were negative with ANA positive in a homogenous pattern. C-reactive protein (CRP) was only slightly raised at 5.6mg/L. Knee aspirate showed mixed inflammatory cells. Radiographs of his spine showed no syndesmophytes but sacroiliac joints showed established bilateral sacroiliitis. A diagnosis of ankylosing spondylitis with secondary LA was made. He was commenced on sulfasalazine to treat his peripheral inflammatory arthritis along with continuation of NSAID. He remained symptomatic with Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) score of 8 and Spinal pain VAS of 9. As he fulfilled NICE guidelines for biologic use in AS, he was commenced on adalimumab 40 mg fortnightly injections and had a good response to treatment with improvement in BASDAI, pain VAS, knee swelling and normalisation of CRP.

Conclusion
There have been reports of LA in association with inflammatory joint disease. This is the first case of bilateral LA as a presenting feature of ankylosing spondylitis. It has been demonstrated that LA plays a role in joint inflammation and damage through tumour necrosis factor alpha (TNFα) and matrix metalloproteinase 3 (MMP3). MMP3 is known to cause joint erosion in inflammatory joint conditions such as rheumatoid arthritis and ankylosing spondylitis. It is therefore proposed that while managing LA, looking for underlying inflammatory arthritis may provide the answer.

Disclosures
S. Khalid None. M. Cox None. M. Kazmi None.