langerhans cell histiocytosis ( lch ) is a rare monoclonal disease , of which incidence rate is 4 to 5 per 1 million individuals , and mortality rate is about 3% in adults .
its clinical presentation is highly variable because it can affect multiple organs , such as lung , bone , skin , lymph nodes , hypothalamopituitary axis , and other multiple sites .
however , due to the fact that involvement of the thyroid either as an isolated mass or as part of multisystemic disease is extremely rare , the diagnosis and therapeutic evaluation for such disease is still controversial . according to preliminary statistics ,
to the best of our knowledge , few studies had reported that the positron emission tomography / computed tomography ( pet / ct ) was used for diagnosis and therapeutic evaluation for lch involving thyroid in detail .
the purpose of this article was to report a case and describe the use of pet / ct to make a diagnosis and therapeutic evaluation for lch involving thyroid .
a 27-year - old man came to our hospital with painless thyroid nodules that had been present for more than 3 months .
he had no symptoms , such as dysphagia , dyspnea , hoarseness , appetite changes , weight changes or palpitations , and no history of thyroid cancer . in the past
thyroid ultrasound showed diffused hypoechogenicity and a 28    13    22  mm hypoechoic nodule on the right side of the thyroid and a 16    7    11  mm hypoechoic nodule on the left .
thyroid function tests were as follows : thyroid - stimulating hormone ( tsh ) : 1.67  miu / l ( 0.354.94  miu / l ) ; free triiodothyronine ( ft3 ) : 5.49  pmol / l ( 3.6710.43  pmol / l ) ; and free thyroxine ( ft4 ) : 11.3  pmol / l ( 7.521.1  pmol / l ) . additionally , calcitonin , parathyroid hormone , thyroglobulin , antithyroglobulin , and antimicrosomal antibodies were also within normal range .
fine - needle aspiration biopsy ( fnab ) showed atypical hyperplasia in thyroid nodule and considered the possibility of langerhans cells infiltration ( figure 1a ) . with the consideration of the thyroid nodules with limitation of cytologic results and lch usually involving multiple systems , additional pet / ct was performed , and the result showed fluorodeoxyglucose ( fdg ) intense accumulation in the thyroid ( suv  =  7.2 ) and in the vertebral body of s12 ( suv value  =  10.7 ) ( figure 2a , b ) .
therefore , according to his symptom and the result of pet / ct , we got a biopsy in the vertebral body of s12 and confirmed the lch by the positive immunohistochemical staining of cd1 and s100 ( figure 1b  d ) .
subsequently , the patient received a series of treatments containing chemotherapy ( 2 cycle vpe  +  mtx [ vindesine 4  mg  +  etoposide 100  mg  +  methotrexate 1.0  g ]  +  1 cycle iae [ ifosfamide 3  g  +  mesna 3.2  g  +  etoposide 100  mg  +  cytosine - arabinoside 200  mg ]  +  1 cycle minibeam [ carmustine 125  mg  +  etoposide 50  mg  +  cytosine - arabinoside 150  mg  +  melphalan 50  mg ]  +  1 cycle beam [ armustine 600  mg  +  etoposide 150  mg  +  cytosine - arabinoside 300  mg  +  melphalan 200  mg ] ) and autologus bone marrow stem cell transplantation .
after about 8 months treatment , pet / ct was performed to evaluate the therapeutic effect , and showed that the suv in vertebral body of s12 ( suv value  =  4.3 ) reduced significantly compared with the previous pet / ct(2015.03 ) ( figure 1e , f ) .
a , fine - needle aspiration cytology of thyroid showed the possibility of langerhans cells infiltration ( 200 ) .
b , the pathologic findings of vertebral body of s1 - 2 showed langerhans cell proliferation ( 200 ) .
e , before treatment , the result of pet / ct ( 2012.03 ) showed intense accumulation in the vertebral body of s1 - 2 ( suv value  =  10.7 ) .
f , after treatment , the result of pet / ct ( 2012.11 ) showed slight accumulation in the vertebral body of s1 - 2 ( suv value  =  4.3 ) .
pet / ct ( 2012.03 ) showed fdg intense accumulation in the ( a , arrow ) thyroid ( suv value  =  7.2 ) and ( b , arrow ) the vertebral body of s1 - 2 ( suv value  =  10.7 ) .
fdg  =  fluorodeoxyglucose , pet / ct  =  positron emission tomography / computed tomography .
the written informed consent for the case report was obtained from this patient , and the consent procedure was approved by the ethics committee of the first affiliated hospital of wenzhou medical university .
langerhans cell histiocytosis can be confirmed as one organ or a systemic disease , with lung , bone , and central nervous system being the most favored sites of involvement .
the incidence of lch involving the thyroid gland either as an isolated lesion or as a part of multisystemic disease is extremely rare . due to the first symptom of lch involving thyroid , which often shows painless thyroid nodules and the lack of other apparent presentations , the lch involving thyroid is very easy to be ignored .
however , it can be confused with other far more common thyroid diseases and the misdiagnosis rate is not low .
considering the lch is a multisystemic disease and has a high misdiagnosis rate , the diagnosis of lch involving the thyroid or multisystem can be a medical puzzle .
although the diagnostic thyroidectomy was considered as an exact diagnostic method for lch involving thyroid , it had a lot of complications after thyroidectomy and had no benefit for multisystem lch .
several publications reported that pet / ct is a competent examination for thyroid nodules with inconclusive cytologic results .
giovanella et al had suggested that pet / ct can be performed for lch . in this case ,
pet / ct was performed to help make an accurate diagnosis of lch involving thyroid .
moreover , it plays an important role to find other potential lch lesions , which has a great guiding effect on the diagnosis of lch . additionally , the fdg uptake is predictive to therapeutic response during the course of cancer treatment and a lot of studies recommended that the pet / ct is of great value in the therapeutic evaluation of cancer treatment . in our case ,
the result of pet / ct suggested that the multisystemic lch had a radiologic remission and a good clinical recovery during the subsequent follow - up period . in clinical settings ,
the diagnosis of lch involving the thyroid or other rare isolated lesions is a challenge , since it is difficult to get ideal biopsy specimens in thyroid nodules for the identification of lch .
according to our clinical practice , some easily ignored lesions , such as bone area , suitable for biopsy and immunohistochemical detection , can be found by the imaging technology of pet / ct . during the treatment of lch
, pet / ct can be performed to assess the therapeutic effect , the therapeutic response , and the surveillance
firstly , the lch involving thyroid is extremely rare and the use of pet / ct for this is unusual . therefore , there are not enough studies to make a literature review of the use of pet / ct in lch involving thyroid . secondly , we only make a case report and sum up some experience of diagnosis and therapeutic evaluation for lch involving thyroid .
more cases should be enrolled to summarize more reliable diagnostic and therapeutic experience . in conclusion ,
when the thyroid nodule fnab results showed the possibility of langerhans cells infiltration , the lch involving thyroid should be considered .
the pet / ct should be kept in mind for lch involving thyroid , which provides evidence to select the most effective and reliable treatment , and contributes to the individualized treatment for lch .
 abstractlangerhans cell histiocytosis ( lch ) involving the thyroid gland is extremely rare . 
 currently , the diagnosis and therapeutic evaluation for lch involving thyroid is a challenge.we reported a rare case of lch involving thyroid , presenting as painless thyroid goiters , and successfully performed positron emission tomography / computed tomography ( pet / ct ) to make an accurate diagnosis and therapeutic evaluation for lch.although the histology or cytology is the golden standard for the diagnosis of lch involving thyroid , the pet / ct should be keep in mind when lch involving thyroid with inconclusive cytologic results . during the treatment of lch 
 , pet / ct can be performed to assess the therapeutic effect and select the most effective and reliable treatment for lch . 