approximately 67% of siadh cases are reported to be caused by cancer , the majority of which ( 70% ) are linked to small cell carcinoma of the lung ( 1 ) .
head and neck cancers are responsible for only 1.5% of siadh cases ; however , the majority of these cases have the histology of small cell carcinoma ( 2 ) .
there have been scant reports of squamous cell carcinoma as a cause of siadh and , even more rarely , squamous cell carcinoma of the head and neck .
this report describes a patient who was found to have squamous cell carcinoma of the nasopharynx and later developed siadh following neck dissection .
a 77-year - old caucasian man presented to the ent clinic with a 3 month history of progressive nonproductive cough .
he had a social history of smoking , one pack a day for 50 yr .
his regular check - up excludes any other possibility for unknown diseases , including renal failure or heart failure .
he had a past surgical history of coronary artery bypass graft ( cabg ) . upon physical examination ,
a biopsy of the mass was ordered and the tissue sample demonstrated transformation to squamous cell carcinoma .
the patient then underwent modified radical neck dissection without sacrificed internal jugular vein , which was carried out by our hospital 's head and neck cancer team . on post - operative day 2 , a doppler ultrasound ( us ) detected deep vein thrombosis ( dvt ) in the patient 's left arm which prompted us to start him on heparin ( lovenox ) . on post - operative day 6
, the patient developed pulmonary edema , and a loop diuretic ( furosemide , lasix ) was then added to his treatment .
the echocardiography showed normal ventricular function . on post - operative day 10 , he presented with lethargy , 2 + peripheral edema and a central venous pressure ( cvp ) of 6 mmhg ( fig .
mmol / l , a serum k level of 4.7 mmol / l , a serum osmolality of 265 mosm / kg , a ph of 7.46 , a pco2 of 53 mmhg and hco3 of 35 mmol / l .
the urine analysis showed an osmolality of 390 mosm / kg , a urinary na of 142 mmol / l and fractional excretion of sodium > 1% .
this was followed by thyroid function tests and an acth stimulation test , the results of which were found to be within normal limits , eliminating hypothyroidism and adrenal insufficiency as possible causes for the patient 's electrolyte disturbance ( fig .
a diagnosis of siadh was established , and the patient was treated with 1 g / day of oral salt and 3% hypertonic saline .
in addition to this , the diuretic was discontinued to avoid aggravating the hyponatremia . by his post - operative day 15
the oral salt was then placed on hold , and 0.9% normal saline was started . on the morning of post - operative day 20 , the patient 's blood pressure temporarily dropped from a normal range to 70/57 mmhg .
however , it was quickly discovered that the patient was mistakenly receiving 0.45% hypotonic saline instead of 0.9% normal saline . at this point ,
the patient had already received approximately 1,320 ml of half - normal saline for 4 hr , and in addition to the drop in his blood pressure , he became confused and then started vomiting .
the half - normal saline was instantly stopped and his serum na was checked , and it was found to be 124 mmol / l .
unfortunately , his clinical condition deteriorated very quickly , with his blood pressure continuing to drop . cardiopulmonary resuscitation ( cpr )
siadh was first described in two patients with bronchogenic small cell carcinoma in 1957 by schwartz ( 3 ) . at the time
, schwartz suggested that small cell carcinoma produced some quantity of antidiuretic hormone , which was later found to consist of arginine vasopressin ( avp ) by bleich hl in 1976 .
bleich also discovered the avp - regulated water channels in the kidneys that were later termed " aquaporins " ( 4 ) .
schwartz 's hypothesis was proven by detecting ectopic avp in small cell carcinoma ( 5 ) .
this hypothesis was further confirmed by expression analysis of the avp - np ii gene , which controls the production of avp , in small cell carcinoma cells .
these findings established the well accepted mechanism of action of siadh caused by small cell carcinoma ( 6 ) . in 1976 , moses was the first to describe siadh in patients with sqamous cell carcinoma , but the mechanism by which it occurs was not discovered and it has not been demonstrated since ( 7 ) . there has not been a proven or widely accepted theory explaining siadh caused by squamous cell carcinoma .
although many researchers have found avp gene not only in small cell carcinoma but also in undifferentiated carcinoma ( 8) and anaplastic carcinoma ( 9 ) , they have failed to find avp gene in squamous cell carcinoma .
this course is stimulated by neuropeptides such as acetylcholine , histamine , bradykinin , angiotensin ii and neuropeptide y ( 10 , 11 ) . in 2004 , lee demonstrated a significant increase of neuropeptide y in the hypothalamus of a mouse that was inoculated with human squamous cell carcinoma ( 11 ) .
these findings led him to suggest that squamous cell carcinoma produced neuropeptide y , which stimulated production of endogenous avp , while small cell carcinoma produced ectopic avp directly .
in addition , there has been more compelling evidence to support lee 's theory , such as the finding of increased avp levels in 38% of siadh patients with squamous cell carcinoma , despite no evidence of ectopic avp ( 12 ) . in the event that neuropeptide y
is detected in siadh patients with squamous cell carcinoma , this hypothesis can be proven clinically .
in addition to siadh association with a number of malignancies ( most notably small - cell cancer of the lung ) , siadh can also occur following head injury , surgery ( following neck dissection and manipulation of the nervous system ) , drugs ( such as morphine , nsaids , and oxytocin ) and in a number of pulmonary ( pneumonia , abscess , and tuberculosis ) and endocrine disease states ( hypothyroidism and glucocorticoid deficiency ) .
it should be considered in patients who are euvolemic and hyponatremic with elevated urine sodium ( usually greater than 20 meq / l ) and urine osmolality .
avp is an antidiuretic hormone that maintains homeostasis against hypotension and hypovolemia , which is sensed by the baroreceptors in the neck .
when these receptors are stimulated , e.g. via neck dissection , serum avp will rise as a result of the signaling from the baroreceptors . in 1997 , mesko observed siadh in 27% of those patients undergoing neck dissection ( 13 ) .
however , when siadh develops in a cancer patient who has undergone neck dissection , it is uncertain whether the siadh is a paraneoplastic syndrome or post - operative siadh .
siadh can be a paraneoplastic syndrome caused by squamous cell carcinoma or a post - operative siadh caused by neck dissection .
therefore , we will conduct further research on the neuropeptides of squamous cell carcinoma , which may help to prevent siadh post - neck dissection .
 the paraneoplastic syndromes include the disorders that accompany benign or malignant tumors but are not directly related to mass effects or invasion by the primary tumor or its metastases . 
 neoplastic cells can produce a variety of peptides that exert biologic actions at local and distant sites and can elicit responses that cause a variety of hormonal , hematologic , dermatologic and neurologic symptoms . almost every type of malignancy has the potential to produce hormones or cytokines or to induce immunologic responses . 
 lung cancers , both non - small cell and small cell , are capable of producing a variety of paraneoplastic syndromes . 
 the majority of such syndromes are caused by small cell carcinomas , including many endocrinopathies . 
 syndrome of inappropriate antidiuretic hormone ( siadh ) has been commonly associated with small cell carcinoma and is often seen in these patients . 
 however , siadh associated with squamous cell carcinoma has rarely been reported on , and the mechanism for this rare association is still unknown . 
 we present here a case of a 77-yr - old man who developed siadh caused by squamous cell carcinoma of the nasopharynx . 
INTRODUCTION
CASE PRESENTATION
DISCUSSION
CONCLUSION