castleman disease ( cd ) is a rare lymphoproliferative disease , which is histopathologically classified into hyaline vascular type , plasma cell type and mixed type . although the cause of this disorder has not been definitely established , chronic low - grade inflammation , immunodeficiency state and autoimmunity are the proposed pathogenetic mechanisms . several autoimmune diseases have been associated with cd , but no association with hashimoto thyroiditis has been defined . the standard for staging of the disease is contrast - enhanced computed tomography ( ct ) . there is insufficient data in the literature about the role of [ f]fluorodeoxyglucose ( fdg)-positron emission tomography ( pet)/ct in staging and evaluating response to treatment . this case report discusses a patient with unicentric mixed type cd associated with hashimoto thyroiditis , for whom staging and evaluation of response to therapy was done with fdg - pet / ct . a 62-year - old woman was admitted to the hospital with atypical chest pain . the physical examination and electrocardiography were normal . the ct scan of the chest revealed multiple mediastinal lymphadenopathies ( laps ) extending from the thyroid level to the aortic root and surrounding the major vascular structures . the pet / ct study showed the presence increased fdg uptake in the perivascular structures of the anterior mediastinum ( fig . also , a diffuse fdg uptake was determined in both lobes of the thyroid gland . as a result , figure 1fdg - pet / ct images at diagnosis : ( a ) selected coronal pet slice , ( b ) corresponding ct slice , ( c ) maximum intensity projection ( mip ) image of pet data . fdg - pet / ct images after treatment : ( d ) coronal pet slice , ( e ) corresponding ct slice , ( f ) mip image of pet data . fdg - pet / ct images at diagnosis : ( a ) selected coronal pet slice , ( b ) corresponding ct slice , ( c ) maximum intensity projection ( mip ) image of pet data . fdg - pet / ct images after treatment : ( d ) coronal pet slice , ( e ) corresponding ct slice , ( f ) mip image of pet data . histological analysis revealed hyaline vascular type cd in one lymph node and plasma cell type cd in 3 lymph nodes . 2 ) . 
 figure 2(a ) the plasma cells and some blood vessels stained with haematoxylin  eosin ( he 20 ) ; ( b ) plasma cells seen in more detail with microscopic zoom ( he 40 ) ; ( c ) plasma cells are positive with cd79a immunohistochemically ( cd79a 20 ) ; ( d ) hyaline vascular variant type , plasma cells are seen in an eosinophilic hyalinized area ( he 40 ) . ( a ) the plasma cells and some blood vessels stained with haematoxylin  eosin ( he 20 ) ; ( b ) plasma cells seen in more detail with microscopic zoom ( he 40 ) ; ( c ) plasma cells are positive with cd79a immunohistochemically ( cd79a 20 ) ; ( d ) hyaline vascular variant type , plasma cells are seen in an eosinophilic hyalinized area ( he 40 ) . laboratory evaluation showed anaemia of chronic disease ( hb 9.3  g / dl ) , elevated erythrocyte sedimentation rate ( 65  mm / h ) , mild elevation of serum igg level ( 17.1  g / l , normal limits 716 g / l ) , and hypothyroidism ( thyroid stimulating hormone 24.98  iu / ml ) . bone marrow aspiration and biopsy showed a normocellular bone marrow with no increase in plasma cell count . antithyroglobulin antibody level was > 4000  iu / ml ( normal range 0115  iu / ml ) and her antithyroid peroxidase antibody level was 331.7  iu / ml ( normal range 034  iu / ml ) . the patient was diagnosed as hashimoto thyroiditis and levothyroxine 0.1  mg was initiated . further evaluation for autoimmune diseases showed no disorders other than hashimoto thyroiditis . due to the close relationship of the laps to the major vascular structures , complete surgical resection was not feasible . as the patient had a medical history of asthma and mild cardiac dysfunction , mediastinal radiotherapy was not considered to avoid cardiac and pulmonary toxicity . the patient received 8 cycles of vincristine ( 2  mg , day 1 ) and prednisolone ( 100  mg , days 15 ) , every 2 weeks . after 8 cycles of chemotherapy , the laps had regressed 30% in diameter on chest ct . f ) . during the 42-month follow - up , no clinical and radiological signs suggestive of recurrence have been seen . cd is a polyclonal lymphoproliferative disease , characterized by lymph node enlargement with distinctive histological and clinical features . it has been divided clinically into unicentric and multicentric types , and histopathologically into hyaline vascular type , plasma cell type and mixed type the hyaline vascular variant is the most common , comprising 90% of cases and is characterized by a benign clinical course . in contrast , the plasma cell variant accounts for 9% of cases and tends to be clinically aggressive . malignant transformation and systemic findings such as fever and anaemia are rare in this variant of cd . the plasma cell variant is generally multicentric and in contrast to the hyaline vascular type , systemic findings are frequently encountered , as well as a high risk of malignant transformation . mixed variant cd is mostly multicentric , however , as in our patient , some patients with unicentric cd reveal features of both hyaline vascular type and plasma cell type . although the cause of cd is unknown ; chronic low - grade inflammation , immunodeficiency state and autoimmunity have been proposed as likely pathogenic mechanisms numerous autoimmune diseases are associated with cd including sjgren syndrome and rheumatoid arthritis . dysregulated interleukin-6 production may play a key role in the pathogenesis of cd . in our case , it is not clear if autoimmunity is the underlying cause of cd , as it has been suggested that cd can alter the immune system and might lead to development of such an autoimmune disease . so , the autoimmune diseases can be the cause or the result of cd . although they may share a common pathogenic pathway related to immune dysregulation , the possibility of a coincidental association must also be raised , especially when the high prevalence of hashimoto thyroiditis is considered . the standard modality for the evaluation of disease extent is contrast - enhanced ct , which shows enhancement due to hypervascularity of the lesions . although the value of fdg - pet / ct in staging has been reported in a few cases , currently the role of fdg - pet / ct in diagnosis and in staging is still controversial . in a case presented by pelosi et al . , it was stated that pet / ct could be considered in staging or restaging the disease and evaluation of response to the treatment . in our case , fdg - pet / ct correctly staged cd at diagnosis and was superior to ct scan in response evaluation . although ct evaluation demonstrated a partial radiological response , the pet / ct revealed complete metabolic response . thus , fdg - pet / ct seems to be useful for both assessment of the extent of the disease and response evaluation . the treatment of cd depends on the extent and in some circumstances on the histological subtype . radiotherapy is the best choice if complete resection is not possible ; especially for the plasma cell variant . in contrast to the unicentric variant , the multicentric variant necessitates aggressive systemic therapy due to its high malignant transformation potential and poor prognosis . the systemic treatment options are immunosuppression , cytoreductive agents , immunomodulators ( steroids , interferon - alpha , thalidomide ) and monoclonal antibodies ( anti - interleukin 6 , rituximab ) . in this case , we achieved a durable complete response with chemotherapy in the absence of local therapy such as surgery or radiotherapy . this case report shows that fdg - pet / ct can have an important role in the staging and evaluation of treatment response in cd . we suggest that due to the rapid progression and high metabolic activity of the mixed type variant and the plasma cell variant , assessment of treatment response can be done with pet - ct . this case is also unique as there no case of cd in association with hashimoto thyroiditis has been reported previously .
abstractcastleman disease ( cd ) is a rare atypical lymphoproliferative disease , pathologically classified as hyaline vascular , plasma cell type and mixed type variant . 
 the underlying cause of cd is unknown , however several theories including autoimmunity have been proposed . 
 we describe a patient diagnosed with unicentric mixed variant cd and hashimoto thyroiditis , concurrently . 
 she was staged with fluorodeoxyglucose ( fdg)-positron emission tomography ( pet)/computed tomography ( ct ) and the disease was localized to the mediastinum . after 6 cycles of chemotherapy consisting of vincristine and prednisone , the mediastinal lymph nodes regressed , but did not disappear from the ct scan . however , fdg - pet / ct showed complete metabolic response . 
 although the role of fdg - pet / ct in staging and evaluation of treatment response is controversial , this case shows that pet / ct can be effective and even better for staging and response evaluation . 
 this case is also unique as there no case of cd in association with hashimoto thyroiditis has been reported previously . 
 however , the possibility of a coincidental association must be raised , especially when the high prevalence of hashimoto thyroiditis is considered .