Can Diagnostic Imaging Help Detect Rare Diseases?

Some rare diseases have symptoms that resemble more common health problems, making them difficult to diagnose. In some cases, doctors need multiple tests to determine the cause of patients' symptoms. Sometimes diagnostic imaging provides clues and reveals abnormal changes in organs, tissues, or body functions that standard tests don't show.

When physicians require additional information to locate abnormal tissue or to inform their understanding of disease activity or its effects on various parts of the body, they order advanced imaging, including an FDG PET-CT scan, a whole body PET-CT scan, and other special scans. The use of advanced imaging and nuclear medicine services at Molecular Diagnostics and Therapy aids physicians in the determination of a variety of medical conditions and in planning treatment.

What Are Rare Diseases?
Rare diseases are diseases that occur in a fairly small number of people. There are thousands of rare diseases, and they impact almost any part of the body. The causes of some rare diseases are related to the genetic makeup, and for others it is related to an immune response, metabolism disorder, a problem with the nervous system, or another organ or tissue. The symptoms differ in each instance. Many rare diseases are not so common and have symptoms that are confused with more common diseases, and this complicates the diagnosis.

Why Can Rare Diseases Be Difficult to Diagnose?
It is also one of the biggest challenges that symptoms aren't specific to one particular disease. For instance, in numerous situations, there is unexplained weight loss, persistent pain or weakness, fever, swelling, or changes in organ function. Doctors then need information provided by blood tests, genetic testing, biopsies, imaging, and other tests to make a diagnosis. However, imaging alone is not usually sufficient to diagnose a rare disease. Instead, once it's in, it provides details that contribute to the physician's understanding of what is happening in the body and determine if further testing is necessary.

How Can PET-CT Help?
PET-CT integrates details of anatomy with information on biological activity. The patient is given an injected amount of radioactive material, and the PET part of the machine measures the pathological distribution of the radioactive waste. This CT information gives details regarding the areas being studied and their structure.

 
Fluorodeoxyglucose (FDG) is a substance similar to glucose that is used in an FDG PET-CT scan. Increased FDG uptake is seen in some tissues and disease processes. Sometimes this information is useful in helping the doctor determine where there may be abnormally active metabolism that needs to be further studied. Increased uptake of FDG, however, is not a confirmation that cancer is present. Other diseases and illnesses, such as infection and inflammation, also exhibit more activity. That is why it is important to take the PET-CT results into account along with all the other test results and the patient's clinical history.

What Is a Whole Body PET-CT Scan?
A whole body PET-CT scan is a single scan that's used to screen a wide area of your body. It gives information on several regions, depending on the clinical situation and scan protocol. In some cases, it is helpful to get information about the distribution of abnormal activity in patients who present with undiagnosed symptoms or those who have an established diagnosis that includes more than one body part. In these patients, a whole-body examination is needed. It also assists physicians to evaluate whether the disease known to them is localized or if other areas of the body should be further scrutinized. Whether or not a whole-body PET-CT should be used is dependent on the clinical enquiry.

Can PET-CT Detect Rare Cancers?
Sometimes, if a cancer is rare, it is possible to detect it with the same imaging tests that are used for most cancers. PET-CT gives more information about metabolism and helps find suspicious areas. In certain cancer patients, an oncology PET-CT scan helps a physician determine the stage of the disease, check for metastasis, and/or determine response to treatment. But a PET-CT scan alone cannot rule out all forms of cancer. However, some tumours do not show high uptake of FDG, and non-cancerous conditions can also be active on a PET scan. Doctors might recommend other imaging tests, lab tests, or a biopsy to make a diagnosis when necessary.

How Does Imaging Help With Rare Non-Cancerous Conditions?
PET-CT and other imaging techniques are not restricted to cancer. Tissues develop abnormal changes due to certain rare inflammatory, infectious, neurological, metabolic, and other diseases that are detectable by specialized imaging studies. In fact, imaging reveals abnormal activity, tissue texture changes, or even involvement of several organs. The results offer further indications to doctors if patients have symptoms that do not have a clear cause. This depends upon which condition is suspected, and the imaging tests vary accordingly.

PET-CT Accuracy and Rare Diseases
When talking about advanced imaging, people want to know how accurate the PET-CT scan is. But there is no universal accuracy percentage for each disease. The performance of PET-CT is influenced by the type of disease being assessed, type of tracer, nature and dimensions of abnormality, patient preparation, image quality, and other clinical factors. Typical PET patterns are not identified in some rare diseases. Some diseases look alike on imaging, and the small lesions are hard to spot. So PET-CT scan findings must be correlated with other imaging findings and taken along with other data and information.

What Other Imaging Tests May Be Used?
PET-CT is only one part of diagnostic imaging. Doctors may also use CT, MRI, ultrasound, X-rays, SPECT, or other specialised examinations depending on the suspected condition. MRI can provide detailed information about soft tissues and is particularly useful for many brain, spine, joint, and other soft-tissue conditions. CT can provide detailed anatomical information and may be useful for examining organs, bones, blood vessels, and other structures. Ultrasound can provide real-time images and is commonly used for several organs and soft tissues. In some cases, combining information from different tests provides a clearer picture.

Why Is the Patient's Medical History Important?
Imaging findings have to be understood in the right clinical context. Doctors may consider the patient's symptoms, duration of illness, family history, previous diagnoses, blood test results, previous scans, and treatment history when interpreting imaging findings. This is particularly important when investigating rare diseases because the imaging appearance may not always be specific. Providing previous reports and relevant medical information can therefore help the healthcare team understand the findings more effectively.

Does a PET-CT Scan Confirm a Rare Disease?
Not always. A PET-CT scan can identify areas of abnormal activity and provide information about where a disease process may be occurring. However, it may not be able to determine the exact cause of that activity. Depending on the findings, doctors may recommend additional tests such as MRI, CT, blood tests, genetic testing, or tissue sampling. A biopsy may be needed in some cases to confirm a diagnosis, particularly when cancer is suspected.

Conclusion
Rare diseases are hard to diagnose as their symptoms manifest themselves in similar ways to more common diseases. Diagnostic imaging gives doctors information about the structure and activity of tissues and helps the doctor find out more when normal tests are insufficient. In certain cases, an FDG PET-CT or whole-body PET-CT or an oncology PET-CT may be helpful; however, a PET-CT should not replace other investigations in the diagnosis of all types of rare conditions.

 
Numerous factors affect the accuracy of PET scanning, such as the disease, the choice of tracer, the protocol used for the scan, patient preparation, and the interpretation of the scan. The combination of imaging and medical history, laboratory studies, and other studies is the best approach. At Molecular Diagnostics and Therapy, advanced imaging technologies are utilized to assist physicians in gaining insight into a subject that aids in the diagnosis, disease assessment, and treatment planning.