A 62-year-old man is evaluated in the ER for drowsiness and generalized weakness for the past 4 weeks. He is brought to the hospital by EMS after he experienced a tonic clonic seizure in a local restaurant. His medical history is positive for HTN and gout, for which he takes metoprolol and allopurinol. He has smoked 1 pack per day for nearly 40 years, with no alcohol or recreational drug abuse. He noticed nearly 20 lb weight loss in past 2 months. Physical examination is normal. Laboratory tests reveal hemoglobin 10.2 gm/dL, leukocyte count 9500/mL, and platelet 171,000/mL. Serum sodium is 122 mEq/L, potassium 3.8 mEq/L, blood urea nitrogen (BUN) 26 mg/dL, and creatinine 0.9 mg/dL. Additional laboratory findings include serum osmolality 258 mOsm/kg, urine osmolality 300 mOsm/kg, and urine sodium 48 mmol/L. TSH and cortisol levels are normal.

Syndrome of inappropriate of antidiuretic hormone (SIADH) is a disorder of impaired water excretion due to excessive secretion of ADH hormone, often by neoplastic cells. Antidiuretic hormone makes the urine concentrated, thereby preventing free water excretion. This leads to water retention and hyponatremia. As total body water increases, the serum osmolality decreases. In normal person, when serum osmolality decreases, the kidneys produce dilute urine to excrete excess water. In SIADH, however, continued ADH release from the tumor prevents urinary dilution, and urine osmolality remains inappropriately high. Urine osmolality more than 100 mOsm/kg in face of hyponatremia is highly suspicious of SIADH. Urine Na value is also higher than 40 mEq/L in SIADH. It is most commonly seen in small cell cancer of the lung.Tumor lysis syndrome (TLS) is an oncologic emergency resulting from breakdown of tumor cells with subsequent release of potassium, phosphate, and uric acid into the circulation. It is most commonly seen in hematologic malignancy such as non-Hodgkin lymphoma or Burkitt lymphoma. Diagnostic criteria (the Cairo-Bishop criteria) for TLS include both laboratory and clinical features. Laboratory TLS includes two or more of the following values: uric acid >= 8 mg/dL, calcium <= 7 mg/dL, potassium >=6 mEq/L, and phosphorus >= 6.5 mg/dL for children or 4.5 mg/dL for adults. Clinical TLS is laboratory TLS plus one of the following: increased serum creatinine concentration (>=1.5 times the upper limit of normal, cardiac arrhythmia, sudden death, or seizure).The classic Trousseau syndrome consists of migratory superficial thrombophlebitis. A single episode of tenderness and inflammation in a superficial vein is common and usually benign, but recurrent unprovoked episodes should prompt a search for an underlying neoplasm Cancer of the pancreas is the most common tumor, but any mucin-producing carcinoma can produce this syndrome. Sezary syndrome is skin infiltration by malignant T-cells in cutaneous T-cell lymphoma. Lambert- Eaton myasthenic syndrome is a disorder of the neuromuscular junction due to antibodies directed against the voltage-gated calcium channel. The antibody prevents normal calcium flux required for the release of acetylcholine, resulting in neuromuscular weakness. It is often a paraneoplastic syndrome associated with small cell carcinoma of the lung