Cancer of the lung kills more people than any other type of cancer, and has been known to kill more people than prostate/colon/breast cancer combined. Although smoking cigarettes is a risk factor, many non-smokers have this deadly condition. Lung cancer has many symptoms, and while most of them are attributable to their mass and subsequent encroachment on other vital organs, other symptoms can be the reason for the patient seeking consultation. These are known as paraneoplastic syndromes, usually associated with small cell lung cancer but occurring with other types as well. The syndromes can usually be divided into hormonal and neurologic subtypes.
Hypercalcemia of Malignancy (HCM)
This is most commonly found in the squamous cell carcinoma type of lung cancer, and is often due to tumor production of a parathyroid hormone-related peptide (pTH-rp). The symptoms are the same as any other condition that causes hypercalcemia--abdominal pain, nausea, vomiting, constipation, thirst, frequent urination, altered mental status--and can result in renal failure from deposition of the excess calcium in the kidneys.
Hyponatremia/Syndrome of Inappropriate Diuretic Hormone (SIADH)
Patients with this syndrome suffer from euvolemic hypo-osmolar hyponatremia that is often unresponsive to conventional treatment. This is most often observed in small cell lung cancer and is due to the excess secretion of antidiuretic hormone (ADH), also known as arginine vasopressin (AVP). Many people, however, don't have excess ADH levels, and in their case the symptoms are a result of excess release of atrial natriuretic peptide (ANP). If conventional hyponatremia treatment fails, the physician can draw blood levels to determine which hormone is in excess as to better tailor therapy for the patient
Cushing Syndrome
This syndrome is the result of ectopic adrenocorticotropic hormone (ACTH) from the tumor, which results in hyperplasia of the adrenal glands and increased levels of cortisol in the body. This is most commonly found in small cell lung cancer and pulmonary carcinoid tumor. Symptoms are usually abrupt in nature, which is attributable to the corresponding rapid growth of the tumor. The patient has hypertension, decreased serum potassium, hyperglycemia and alkalosis, with the characteristic physical findings (striae, "moon facies") usually absent because they are more gradual in nature when developing.
Lambert Eaton Myasthenia
This syndrome is caused by autoantibodies against presynaptic calcium channels in the neuron. Calcium is the signal for acetylcholine release at the neuromuscular junction, and as a result the patient has muscle weakness (usually lower extremities), depressed deep tendon reflexes and occasional autonomic system dysfunction. As opposed to patients with myasthenia gravis, repetitive effort results in improved strength and can be definitively diagnosed by electrophysiological testing.
Paraneoplastic Encephalitis/Sensory Neuropathies
These are due to antineuronal antibodies that affect sensory and motor nerves, frequently causing significant disability. If the antibodies affect the limbus, behavioral changes, amnesia and hallucinations can occur. The antibodies can affect any part of the brain. Serious symptoms can occur, including dysphagia, ataxia and even depressed respiratory function--which can require assisted ventilation of the patient.
Paraneoplastic Cerebellar Degeneration
This is also due to autoantibodies, and often starts with one-sided loss of coordination. This can progress very rapidly to include both sides of the body. Other symptoms can include ataxia, dysarthria, nystagmus. Symptoms tend to stabilize after awhile, but the patient is usually left seriously disabled. Treatment of the tumor does not alter the course of the neurologic paraneoplastic syndromes, with the exception of Lambert Eaton myasthenia.
Considerations
Lung cancer is deadly. It can be very disabling and impart immeasurable suffering to its victims. Do not take the information above as a sign of impending cancer. If you or anyone you know has suspicious symptoms, consult a doctor.
References
- Abeloff's Clinical Oncology, 4th ed. Abeloff 2008
- Chest. "Initial Evaluation of the Patient With Lung Cancer: Symptoms, Signs, Laboratory Tests, and Paraneoplastic Syndromes ACCP Evidenced-Based Clinical Practice Guidelines (2nd Edition)." Spiro S, Gould M, Colice G. Volume 132, Issue 3 (September 2007)
- New England Journal of Medicine."Paraneoplastic Syndromes Involving the Nervous System." Darnell R, Posner J. Volume 349:1543-1554 October 16, 2003
