Many patients who are diagnosed with small cell lung cancer are symptomatic at presentation but have been symptomatic for less than three months. Small cell carcinoma causes a number of paraneoplastic syndromes. Small cell carcinoma is the most common type of cancer to cause clinical hormone syndromes. The symptoms of Cushing's syndrome are nonspecific and are often attributed to other factors. This is caused by secretion of ADH from the tumor.
Symptoms are related to the plasma hypotonicity that is secondary to water retention.
Symptoms include weakness, lethargy, abnormal mentation, coma, and seizures. Laboratory evaluation shows inappropriately high urine osmolality. Another paraneoplastic syndrome associated with small cell carcinomas is the Eaton-Lambert syndrome, also known as myasthenic syndrome. It is characterized by fatigability, proximal muscular weakness, dry mouth, muscle discomfort, and paresthesias. Unlike myasthenia, however, Eaton-Lambert is associated with improved strength with repeated muscle activity.