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Editor,—We present the unique case of a patient with an isolated plasmacytoma of the episclera mimicking a painful episcleritis. Plasmacytomas usually grow in the bone marrow probably because of their special homing receptors1—for example, α4β1 integrin.2 Solitary plasmacytic tumours outside the bone marrow are rare. They mostly involve the oropharynx and the upper respiratory tract, but have also been encountered in the lids, the orbit, and the palpebral conjunctiva.3-5 Only one case of a solitary epibulbar plasmacytoma with intraocular invasion has been reported yet.6
A 61 year old patient presented with an ”inflammatory” episcleral nodule within the lower temporal quadrant and mild pain in his left eye (Fig 1), which had already lasted 5 months and had been diagnosed as episcleritis. There was no evidence of rheumatic disease; ANA and ANCA were negative. Neither dexamethasone eyedrops nor oral fluocortolone (60 mg) were helpful, thus an excisional biopsy was performed. The tumour seemed to be attached only to Tenon's capsule and could easily be removed.
Surprisingly, the histopathological examination revealed a monomorphous infiltrate of plasma cells with characteristic eccentric nuclei and basophilic cytoplasm (Fig 2). The cells stained positively with the plasma cell marker VS38 and showed a kappa light chain restriction. The proliferation rate was increased with an MIB1 positivity of 5%. Immunohistochemistry for CD20, IgA, IgD, and IgG was negative.
Three months later an IgA lambda monoclonal gammopathy with an IgA level of 5.6 g/l (normal 0.7–4.0 g/l) was found, but neither bone marrow biopsy nor bone scan showed any abnormalities. A local recurrence of the episcleral tumour with infiltration of the lateral rectus muscle 6 months after the initial diagnosis, was irradiated with 46 Gy over 2 months. The tumour resolved completely and did not recur. The IgA level of the serum ranged between 5.2 and 6.7 g/l over a period of almost 3 years.
Our case is unique in several respects. The isolated extramedullary plasmacytoma of our patient mimicked an episcleritis with mild pain and inflammatory reaction. As it turned out to be resistant to anti-inflammatory therapy a biopsy was performed which finally allowed for the correct diagnosis. Thus solitary plasmacytoma has to be included in the spectrum of ocular masquerade syndrome.7
Another interesting aspect is that our patient developed a monoclonal gammopathy, apparently not related to the isolated episcleral plasmacytoma. The latter showed a kappa light chain restriction, whereas in the serum the level of IgA lambda was increased. As a thorough general examination did not reveal any signs of systemic disease or isolated plasmacytoma elsewhere, the monoclonal component was attributed to a monoclonal gammopathy of unknown significance (MGUS) which is considered as a benign or premalignant disorder.
Lymphocytes and plasma cells of the MALT, especially the GALT, are characterised by integrin α4β7,8 instead of integrin α4β1 which is displayed by plasma cells homing to the bone marrow.2 According to this extramedullary plasmacytoma tend to occur more often in the MALT or GALT than in other locations except for the solitary plasmacytoma of the bone. Ninety per cent of the isolated plasmacytomas grow in the head and neck area, especially in the upper respiratory tract, but they are surprisingly rare in the gastrointestinal tract,9though 80% of all immunoglobuline producing cells of the body are located here.10 The atypical location of the plasmacytoma presented here may be mediated through a specific repertoire of adhesion molecules. Since antibodies for detection of the above mentioned homing receptors in paraffin sections are not available until now, we were not able to find out whether special integrins or a total loss of them was responsible for the peculiar location of the tumour in our patient. It may only be speculated that the isolated plasmacytoma in our case arose from a monoclonal proliferation of plasma cells in an originally inflammatory infiltrate. Whether tissue specific immunoregulatory mechanisms involving accessory cells are also implicated in the localised episcleral tumour growth remain to be elucidated.
We thank Mrs Renate Buchen for technical assistance, Dr Sarah Coupland for providing the VS38 immunostaining, and Dr Flemming Staubach for reading the manuscript.