a 50 year old female machinist presented to our general orthopaedic outpatients department with a 5 month history of right groin and buttock pain of spontaneous onset . the pain radiated to the right knee and had progressively worsened over the preceding month . she had not experienced any constitutional symptoms , had no previous malignancies , and had been on a daily dose of 20  mg prednisone and 150  mg azathioprine for 4 years as part of her treatment for sarcoidosis . an anteroposterior ( ap ) radiograph of the pelvis and lateral radiograph of the right hip demonstrated moderate degenerative changes of both hips ( fig . 1 , fig . 2 ) . a provisional differential diagnosis of early avascular necrosis ( avn ) or femoroacetabular impingement ( fai ) was made . renal function and calcium , magnesium and phosphate ( cmp ) levels were normal , c - reactive protein was 8.5 an mri revealed no evidence of avn , with areas of intermediate to high signal in the right femoral head and neck , as well as the left femur and pelvis ( fig . further clinical work up was recommended to exclude other causes such as metastatic lesions or myeloma if clinically indicated . by this time the patients symptoms had continued to progress , and a second ap pelvis x - ray ( fig . 5 ) revealed a lytic lesion in the inferior neck of the right femur with a mirels score of 11 . after consultation with both the musculoskeletal tumour and arthroplasty units , it was decided to perform a biopsy of the femoral head / neck and total hip replacement as a single stage procedure . uncemented acetabular and femoral components were used , with a ceramic - on ceramic bearing surface . macroscopic examination of the excised femoral head confirmed a 1713  mm lytic lesion in the inferior neck . histological analysis of the femoral head showed hypercellular bone marrow with diffuse replacement of marrow spaces by a population of mature plasma cells . in addition , scattered non - necrotising granulomas consistent with sarcoidosis were present ( fig . bone marrow aspiration , biopsy and serum protein electrophoresis confirmed the diagnosis of multiple myeloma ( fig . the patient was referred to the department of haematology , where treatment with high dose dexamethasone and cyclophosphamide was started . at most recent follow - up 5 months post surgery the patient had an asymptomatic right hip with no change in component position ( fig . 10 ) , and no progression of the lesions in her left hip and pelvis . the patients clinical and biochemical response to the myeloma treatment has been good , with a drop in the igg lambda monoclonal peak from 80 autologous haemopoetic stem cell transplant is planned after maximal response has been achieved with cyclophosphamide and dexamethasone . sarcoidosis is an inflammatory disorder of unknown aetiology characterised by the presence of non - caseating granulomas , with no evidence of other known causes of granulomatous disease . it involves multiple organs , most commonly the lungs , lymph nodes , skin , and eyes , but may be present in any organ system . involvement of the musculoskeletal system is well described in the literature . up to 35% of patients will develop an acute or chronic polyarthropathy , and skeletal muscle granulomas occur in 80% of patients , but are largely asymptomatic . skeletal lesions are typically bilateral and most commonly seen in the small bones of the hand and feet with associated skin lesions . lesions of the axial skeleton and long bones are considered uncommon , and occur in approximately 5% of patients , . neither skeletal surveys nor radio - isotope scans have proved reliable in screening for skeletal lesions . the lesions are typically small cysts with minimal involvement of adjacent soft tissue , but may present as an active lytic or sclerotic lesion or pathological fracture . mri features are of indistinct or well marginated lesions of varying sizes with decreased intensity on t1 weighted images and increased intensity on t2 and proton - density fat - saturated weighted images , and lesions may enhance after contrast . there are no pathognomonic features of skeletal sarcoidosis on mri , and the differential includes metastastatic disease , lymphoma , myeloma and disseminated tuberculosis . moore et al . , in a study of 40 patients with sarcoidosis and musculoskeletal symptoms , found intramedullary bone lesions on mri in 43% of patients ( 17/40 ) . lesions of the large bones and axial skeleton were present in 33% of patients ( 13/40 ) , 9 of which were multiple and 4 solitary . two patients ( 5% ) were coincidentally found to have mri findings of avn of the hip , both of whom were on corticosteroids . less than half of the patients had biopsies of the lesions , all of which demonstrated non - caseating granulomas consistent with sarcoidosis . the association between sarcoidosis and myeloma is poorly understood . in a review of the literature , the median interval from the time of diagnosis of sarcoidosis to that of multiple myeloma was 6 years which was similar to the interval of 5 years in our patient . they found that the median age at diagnosis of sarcoidosis was 56 years which was significantly older than that of the general patient population with the disease . the patient in our case report was diagnosed with sarcoidosis at a more typical age of 45 years . in a review of the literature , brincker found 145 patients with sarcoidosis who had developed a malignant neoplasm , including 66 cases of various types of lymphoproliferative disorders , . there is evidence that patients with sarcoidosis have immune system dysregulation , including activation of cd4-positive t - helper cells , increased secretion of cytokines , and decreased cd8-positive t - suppressor cells , . the defective t - cell suppression and increased cytokine secretion hunninghake et al . showed that patients with sarcoidosis have greater ratios of igg and igm secreting cells compared to normal individuals . they demonstrated that b lymphocytes in normal individuals , when cultured with t lymphocytes from patients with sarcoidosis , were induced to differentiate into immunoglobulin - secreting cells . the extended half - life of b lymphocytes and plasma cells in sarcoidosis patients may also increase their risk of undergoing neoplastic transformation . in a review on skeletal sarcoidosis , moore et al . recommended that in a patient with proven sarcoidosis , biopsy of musculoskeletal lesions detected at mri may not be necessary . however , they added that in some patients in whom sarcoidosis was not proven or a second comorbidity was suspected , a biopsy should be undertaken . many patients with sarcoidosis will present with anaemia and fatigue , either as a result of the primary disease or as a side effect of treatment . mri scans and possible subsequent biopsies in all patients with sarcoidosis and musculoskeletal complaints would place a large strain on resources . we believe a high index of suspicion and good clinical judgement is required when patients with sarcoidosis present with musculoskeletal pain , and there should be a low threshold for further investigation . serum calcium , total protein and albumin levels and possibly serum protein electrophoresis would assist in diagnosing or excluding multiple myeloma . mri is of limited value as it does not differentiate skeletal sarcoidosis from myeloma , lymphoma , metastatic disease or disseminated tuberculosis . we describe a patient with sarcoidosis who subsequently developed multiple myeloma to raise awareness of this association . the explanation for this association is not known , however immune dysregulation may be involved in the pathogenesis . orthopaedic surgeons need to be aware of the association and the possibility of dual pathologies to avoid missing the diagnosis of multiple myeloma in patients with sarcoidosis . a high index of suspicion and good clinical judgement is therefore required when patients with sarcoidosis present with musculoskeletal pain , and there should be a low threshold for further investigation . informed consent was obtained from the patient for publication of this case report and accompanying images . university of cape town : department of surgery , departmental research committee , approval number 2013/069 .
the association of sarcoidosis with multiple myeloma is not well known . including this case report , 
 12 cases of patients with both sarcoidosis and multiple myeloma have been reported in the literature . 
 the skeletal lesions of both conditions have many clinical and radiological similarities , and unless clinicians are aware of the association and the possibility of dual pathologies , the diagnosis of multiple myeloma in patients known with sarcoidosis may be missed . 
 we present a case of a patient known with longstanding sarcoidosis who was found to have multiple lesions on magnetic resonance imaging ( mri ) involving the pelvis and both proximal femurs . 
 histological analysis revealed the presence of both non - necrotising granulomas consistent with sarcoidosis , and sheets of plasma cells consistent with a plasma cell neoplasm .