1Rheumatology Department, Queen Alexandra Hospital, Southwick Hill Road, Portsmouth and 2Rheumatology Unit, Royal Cornwall Hospital, Truro, UK
Correspondence to: D. G. Hutchinson, Rheumatology Unit, Royal Cornwall Hospital, Truro, Cornwall TR1 3LJ, UK. E-mail: david.hutchinson{at}rcht.swest.nhs.uk
SIR, A 65-yr-old gentleman presented with a 3-month history of a painful, swollen left knee associated with left inguinal lymphadenopathy. There had been no symptoms of weight loss or fevers. There was a background of longstanding ankylosing spondylitis associated with inflammation of his left knee, requiring arthroscopy in 1984. This had shown extensive synovitis but nothing more specific on biopsy. The knee symptoms resolved over a period of months.
A plain film of the left knee had shown some bony destruction associated with an apparent large effusion. Clinically there was a large effusion but aspiration of fluid was difficult and the synovium had a wooden quality to it. The synovial fluid was bloodstained and no malignant cells were seen. The total white blood cell count was 1.3 x 109/l (polymorphonuclear cells 26%, monocytes 3%). Markers of inflammation were raised only modestly, erythrocyte sedimentation rate was 21 mm/h and C-reactive protein concentration 25 mg/l. The full blood count was normal and lactate dehydrogenase 361 U/l (normal range 211423). An MRI scan demonstrated bony erosion with bone marrow oedema affecting the distal femur anteriorly and the medial femoral condyle and the tibia in the intercondylar region (Fig. 1). There was gross synovial hypertrophy affecting the suprapatellar pouch. A 3-cm mass was seen posterior to the femur; it had similar signal characteristics to synovium but no connection with the joint could be seen. This was thought to be an enlarged popliteal lymph node. Arthroscopy was undertaken and synovial biopsies were taken, which revealed a diffuse infiltrate of cells with irregular and kidney-shaped nuclei. The infiltrate appeared to be inflammatory. Reticulin stain showed fibres around groups of cells rather than around individual cells. The tumour was strongly positive for LCA (leucocyte common antigen), L26 and CD79a. There was some CD68 and spotty CD3 positivity. VS38 was also positive. Immunochemistry showed the cells to be predominantly B cells, all T-cell markers being negative. The histological appearances were those of a diffuse large B-cell non-Hodgkin's lymphoma.
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Six courses of chemotherapy (CHOP) and five courses of anti-CD20 therapy (rituximab) resulted in a dramatic response, with his knee returning back to normal.
In NHL there can be skeletal involvement in up to 25% of cases. Synovial involvement is less common and is usually due to direct extension from bone [1]. In this case the synovium was felt to be the primary site of the tumour due to the extent of the synovial hypertrophy compared with the amount of bony involvement. There have been few cases of primary synovial extranodal NHL reported in the literature and only two cases of lymphoma reported in association with ankylosing spondylitis, neither affecting the knee [2, 3]. The MRI appearances of synovial involvement from NHL have only been reported once in the literature [4].
The authors have declared no conflicts of interest.
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References