Diagnosis of Sarcoidosis
Diagnosing sarcoidosis involves eliminating other similar lung disorders, such as tuberculosis or chronic beryllium disease. This is usually done by a thorough clinical and radiological (x-ray) evaluation.
Sarcoidosis is confirmed when there is histological evidence of noncaseating granulomas and other causes have been excluded. A skin test called the Kveim-Siltzback test may be employed in atypical cases when biopsy is not possible. The use of the Kveim-Siltzback test is exceptionally rare in the United States.
Because most sarcoidosis cases involve the lungs and thoracic lymph nodes, the chest x-ray is one of the most helpful diagnostic tools. If sarcoidosis is suspected following chest x-ray, tissue samples are usually collected.
Initial laboratory evaluation of a patient with suspected sarcoidosis includes: chest radiography, pulmonary function tests, electrocardiography, ophthalmologic evaluation, and blood tests (including hepatic, renal, and calcium). Electrocardiograms (ECGs) are often performed to rule out rhythm disturbances caused by sarcoid involvement of the heart.
Other Disorders that Mimic Sarcoidosis
According to the National Jewish Medical and Research Center, some cases thought to be sarcoidosis may actually be an inflammatory response to metal, or another environmental illness. For example, chronic beryllium disease (also known as chronic berylliosis) presents with similar symptoms. Sometimes it is helpful to review a patient's occupational history to see if there are any metals or other environmental toxins that may be causing the same sort of granuloma development.
The diagnostic work up may include:
- Medical History
- Chest xray
- CT Scan
- Pulmonary Function Test
- Eye Exam
- Blood Tests
- Kveim-Siltzback Test
Medical History & Sarcoidosis Diagnosis
Sarcoidosis is usually asymptomatic, meaning that there are no detectable symptoms, and often is suspected only after a chest x-ray or other test. Sometimes, however, a patient experiences sarcoidosis-related problemsa dry cough that persists, excessive tearing, or a skin rash.
The medical history involves asking the patient about any noticeable symptoms that might be related to sarcoidosis. A patient's race and age are also important clues. For example, because the frequency of sarcoidosis among African Americans is so much greater than in Caucasians, doctors should be alert for the possibility of this diagnosis when examining an African American patient.
Chest X-ray & Sarcoidosis Diagnosis
Although there is no one test that can indicate sarcoidosis absolutely, the chest x-ray comes closest. It provides a picture of the lungs and surrounding lymph nodes, which the doctor or radiologist examines for signs of swollen lymph nodes or infiltration (granulomas) in the lungs.
CT Scan & Sarcoidosis
High resolution computed tomography (CT scan) can provide a better look at the lungs and thoracic lymph nodes than conventional x-ray. It allows a more detailed look at the tissue in which granulomas typically form. CT scan is not necessary in most cases.
Pulmonary Function Tests (PFT) & Sarcoidosis Diagnosis
Pulmonary function tests evaluate how well the lungs are functioning (i.e., how well the lungs expand and how much oxygen they are capable of handling). Sarcoidosis patients who have granulomas or fibrosis in their lungs generally do not perform as well as they should on these tests. The lungs do not hold as much air, do not expand as easily, and oxygen and carbon dioxide do not move as easily across the air-blood barrier.
One of the most common PFTs uses an instrument called a spirometer. The patient breathes into a machine that measures changes in the size of the lungs as the person inhales and exhales. It also indicates whether or not there is any obstruction in airflow.
Other PFTs measure how much gas is being exchanged (how much oxygen from inhaled air crosses into the blood, and how much carbon dioxide crosses from the blood into the air exhaled). In patients with sarcoidosis, gas exchange may occur at lower than normal.
Eye Exam & Sarcoidosis Diagnosis
The clinical exam includes a detailed eye exam with a slit-lamp exam, which involves using a special lighting system and microscope to look into the front of the eye and search for abnormalities. Eye exams should be regularly scheduled for all sarcoidosis patients, even if they do not show eye symptoms when diagnosed. Eye symptoms may show up later and, if left untreated, can have serious consequences.
Blood and Biochemistry Tests & Sarcoidosis Diagnosis
In sarcoidosis patients, blood tests can reveal various blood cell abnormalities.
Hypercalcemia and hypercalciuria are abnormally high concentrations of calcium in the blood and urine, respectively. They are often associated with sarcoidosis, but can be caused by a variety of disorders.
Hyperglobulinemia is an abnormally large amount of globulins (a type of protein) in the blood and may be associated with sarcoidosis.
Bronchoscopy & Sarcoidosis Diagnosis
Bronchoscopy is a procedure that involves inserting a flexible tube through the mouth or nose, into the airway, and into the lungs. It enables the doctor to view the tissue inside the lungs (either directly or on a TV monitor) and biopsy (collect a small sample) abnormal tissue for microscopic examination. The procedure is painless (patients are given relaxation medication and a local anesthetic) and normally takes from 15 minutes to an hour.
Complications are rare and include nosebleed, vocal cord injury, temporary lack of oxygen, heart injury (due to either the lack of oxygen or to medication), bleeding from the sample site, and a punctured lung.
Biopsy of lung tissue is very helpful in the diagnosis of sarcoidosis. Patients with a completely normal chest x-ray have a positive diagnosis 50 to 60 percent of the time. Patients with an abnormal chest x-ray have a positive diagnosis 85 to 90 percent of the time.
Other Types of Biopsies & Sarcoidosis Diagnosis
Sometimes a lymph node, liver, or skin biopsy may be necessary to aid in the diagnosis and eliminate other possibilities. These tissue samples have a higher false positive rate than lung biopsy.
Kveim Test & Sarcoidosis Diagnosis
A Kveim test (also known as a Kveim-Siltzbach test) is a skin test that was designed specifically for diagnosing sarcoidosis. It involves collecting lymph node or spleen samples. The sample is processed to eliminate infectivity and is injected into the patient's skin.
Approximately 4 weeks later a skin biopsy is performed; specific histological changes are considered confirmatory for sarcoidosis. The test is poorly standardized and is rarely used in the United States. It may have a role in atypical cases where tissue is difficult or impossible to obtain, such as in neurosarcoidosis.