br Discussion Primary lymphoma of bone is a rare
Discussion Primary lymphoma of bone is a rare disease, first described by Oberling in 1928 and he labeled it as reticulum cell sarcoma of bone because of the presence of characteristic reticulin fibers within the lesion . This work was followed by Parker and Jackson and later by Ivin and Boston who, eventually established the distinct entity of this lesion and labeled it as the malignant lymphoma of bone [6,7]. The use of immunohistochemistry in highlighting the cellular origin of these lymphomas was described by Vassallo in 1987 . Even till today, the diagnosis of these lesions remains challenging and requires the help of immunohistochemical markers along with histopathology to lead to the final diagnosis. The definition of PLB varies throughout the literature. Generally, this entity is defined as malignant lymphoma arising within the medullary cavity of a single bone without concurrent regional lymph node or visceral involvement . In contrast, Shoji and Miller permitted regional lymph node metastases but stipulated that the interval between the onset of symptoms of the primary focus and the appearance of distant metastases should be greater than 6 months . The vast majority of these lymphomas are non-Hodgkin lymphoma (NHL), the common subtype being diffuse large B cell lymphoma. In addition to DLBCL, other lymphoid malignancies may manifest with primary bone presentation, including atypical Burkitt\'s lymphomas, follicular lymphoma, small B-cell lymphomas, B-cell lymphoplasmacytic lymphomas, anaplastic large cell lymphomas, peripheral T-cell lymphomas, HL and precursor B-cell lymphoblastic lymphomas . Primary Hodgkin lymphoma (HL)of bone is extremely rare, and the majority of patients have concurrent nodal involvement at presentation . Clinically, the most commonly affected age group is 20–50 years with a male preponderance (male: female=3:2). Femur (29%) is the most common site affected followed by pelvis (19%), humerus (13%), skull (11%) and tibia (10%) . Heyning FH  reported DAPTinhibitor cost to be the most common site of involvement whereas Susnerwala et al.  found pelvis to be the most common site which is consistent with our study. Three out of five cases had involvement of pelvis. Median age of diagnosis was 37 years with male:female ratio 4.9:1 in study by Susnerwala et al.  whereas median age of diagnosis was 56 years with male:female ratio of 4:1 in our study. Local pain and swelling are usually the most common presenting complaints  but multiple discharging sinuses has rarely been seen as a feature as was seen in one of our cases which was misleading towards an infectious etiology. Radiologically, there exists a wide spectrum of findings ranging from a normal appearing bone to an extensive, destructive or infiltrative lesion. The destructive lesions are patchy, radiolucent, mottled, moth eaten and occasionally exhibit complete loss of the outline. This may be accompanied by cortical bone thickening and destruction in 25% of cases and occasionally large soft-tissue extension . Apart from histopathology, which still remains the mainstay of diagnosis, numerous investigations which aid in diagnosis are skeletal survey, bone scan, bone marrow biopsy, CT scan of whole abdomen and chest to assess lymph node involvement and serum LDH estimation done as part of the staging procedure. With the combined use of CT, MRI and now PET scan, a higher proportion of patients are diagnosed with stage IV disease . The differential diagnosis of PBL are metastatic carcinoma, Ewing\'s sarcoma, osteosarcoma, eosinophilic granuloma (skeletal) and chronic osteomyelitis  and needs to be differentiated from them. The present study emphasizes that it is the wide range of immunohistochemical markers that offers the final rescue in cases with atypical morphology. PBL was defined as a separate disease entity in the realm of lymphoma on the notion of a comparably favorable outcome. This tumor has a significantly different clinical course and a much better prognosis than Non-Hodgkin\'s Lymphoma (NHL), secondarily affecting bone. Radiotherapy is an effective modality for good local control due to its radio-responsiveness, but distant failures occur in approximately 50% of initially localized bone tumors. Thus employment of adjuvant systemic chemotherapy in a multimodality approach is warranted for improvement of results .