Following the incisional biopsy, the patient was diagnosed with SIADH on the grounds of low sodium (124 mEq/l) with low plasma osmolarity (271 mOsm/l), high plasma ADH levels (26.2 pg/ml; reference range, 0.3–3.5 pg/ml), high urine sodium (39 mEq/l) and high urine osmolarity (301 mOsm/l)without dehydration. This evidence concerns the gene AVP and inappropriate ADH syndrome.