PET-CT A Tool To Diagnose Inflammation

Inflammation is defined as a protective response generated by our body at the site of an injury or a tissue which has undergone destruction. This response aids to either destroy or dilute the invaders or create a wall between the injured tissue and the injurious agent.

An injurious agent can be any pathogen, a dust particle, pollen grain, or any food constituent, etc. These foreign antigens can enter the body through mouth, while breathing, through a wound, through insect bite, etc. Our body exhibits inflammation in various ways; the most common ones include pain, swelling, and redness of the skin. The extreme form of inflammation includes the loss of functions by the affected organ. Although an inflammatory response is instigated by an infection, it is a result of attack by our body to the infection so as to get rid of it. The inflammatory response is purely ruled by fighter cells of our body, i.e. the white blood cells and more specifically the neutrophils. This response is a component of innate immunity wherein the neutrophils are directed towards the site of infection, then these neutrophils generate a cascade of chemical reactions which aid in the removal of the pathogen.

Inflammation is classified into two types viz. acute inflammation, which is an outcome of the initial inflammatory response where movement of the plasma and neutrophils at the site of injury occurs, followed by various biochemical reactions. Type two being, chronic inflammation wherein the inflammation prolongs and the neutrophils present at the site of inflammation are replaced by the macrophages & the lymphocytes. An acute inflammation is characterized by pain, swelling, redness, etc. at the site of inflammation, while a chronic inflammation is mostly found to arise either from a prolonged infection or due to an inappropriate response of the immune system which leads to autoimmune diseases.

PET-CT a tool to diagnose inflammation
PET-CT (Positron emission tomographycomputed tomography) is a technique which combines the functional information from the PET scan with the structural information obtained from CT scan. FDG-PET (Fludeoxyglucose PET) combined with CT scan has proved to be a powerful imaging technique in the field of cancer diagnosis. Besides cancer diagnosis, FDG-PET/CT has also gained importance in diagnosis of inflammatory diseases and for monitoring therapies in particular. There has been enough study on the use of FDG-PET/CT in diagnosis, management and follow-up in patients suffering from inflammatory diseases like, sarcoidosis, spondylodiscitis and vasculitis. FDG-PET/CT has also been used in diagnosis of other inflammatory diseases like, rheumatoid arthritis, autoimmune pancreatitis and Inflammatory Bowel Diseases.

Sarcoidosis
It is an inflammatory disorder, characterized by collection of abnormal chronic inflammatory cells in different organs of the body, leading to formation of nodules. The potential cause of sarcoidosis is not confirmed; however, one or more infectious agents could be the potential cause of sarcoidosis. Since sarcoidosis is a multisystem granulomatous disorder, its diagnosis cannot be specific. The diagnosis of sarcoidosis using PET-CT proves useful in selection of the biopsy sites by enabling a proper identification of the affected organ. FDG activity is largely observed in the lymph nodes and the pulmonary parenchyma where there is an inflammation.

Spondylodiscitis
Inflammation of one or more intervertebral disc spaces and vertebrae adjacent to the intervertebral spaces results into Spondylodiscitis. The main causative agents of spondylodiscitis are Staphylococci and Mycobacterium tuberculosis and the disease mainly develops in individuals who are immunocompromised. PET-CT is found to be highly sensitive in diagnosis of spondylodiscitis and also differentiates the disc infection. PET-CT is also efficient in monitoring the therapeutic response in patients suffering from spondylodiscitis.

Vasculitis
Vasculitis is characterized by the destruction of arteries and/or veins due to inflammation, primarily caused due to migration of the WBCS. PET-CT has proved to be useful for the diagnosis of vasculitis in patients with non-specific symptoms. It also aids in identification of areas with an increased FDG uptake so that a biopsy can be done. PETCT also helps in evaluating the extent to which the disease is caused and also the response of the patient towards the treatment.

Rheumatoid arthritis
Rheumatoid arthritis is a systemic autoimmune inflammatory disorder that mainly affects the joints. PETCT is used for evaluation of the activities of the disease, the sites where the disease is found and the response of the treatment towards rheumatoid arthritis. The FDG molecules used for diagnosis purpose in PET-CT show high activity in synovium (connective tissue of joints) of the affected joints.

Autoimmune pancreatitis
It is a type of chronic pancreatitis which is characterized by inflammation of the pancreas. Autoimmune pancreatitis is not quite distinguishable from pancreatic carcinoma (PC). PET-CT aids in differentiating autoimmune pancreatitis from pancreatic cancer. This is achieved by assessing the pattern of FDG uptake in the pancreas and the extra pancreatic lesions. PETCT also has the potential to assess the disease activity of autoimmune pancreatitis and that of extra pancreatic lesions.

Inflammatory bowel disease
Inflammatory bowel disease is an autoimmune disease which is characterized by the inflammation of the colon and the small intestine. The major types of inflammatory bowel diseases are Crohn's disease (inflammation of any part of the gastrointestinal tract) and ulcerative colitis (inflammation of the colon). PET-CT is used to efficiently diagnose different types of inflammatory bowel diseases.

Technology has grown, so has the need. It is time our smart world takes advantage of it!