Rheumatic Diseases: The Role of Total Body MRI in Diagnosis
Particularly for inflammatory joint diseases (rheumatic diseases), total-body MRI has become the diagnostic method of reference to the extent that it has entered all diagnostic guidelines
Rheumatic diseases are a large group of pathologies that involve the osteoarticular system with varying frequency.
Rheumatic diseases predominantly affecting the joints are divided into two broad categories
- non-inflammatory joint diseases (the most common is arthrosis in which there is a mechanism of joint degeneration with no or minimal inflammatory component);
- inflammatory joint diseases in which, conversely, the characterising element is inflammation (the most common and well-known are rheumatoid arthritis, gouty arthritis, psoriatic arthritis and spondyloarthritis).
For the latter group of diseases, Nuclear Magnetic Resonance Imaging (MRI) is probably the most comprehensive diagnostic method, as it is able to see all inflammation-related manifestations such as effusion, synovitis and bone oedema with high sensitivity.
In clinical practice, it is rarely used for peripheral joints (hands, wrists, knees, feet, shoulders, hips) as for these sites ultrasound has proved to be an excellent performer with greater practicality and simplicity, while for inflammatory involvement of the spine, typical of a group of pathologies called spondyloarthritis, MRI has become the diagnostic method of reference so much so as to enter into all diagnostic guidelines.
Moreover, given that in the last 20 years MRI, in its particular application called total-body MRI (WBMR: whole body Magnetic Resonance), has been widely studied and used in the oncological field to study neoplastic localisations of the skeleton, thanks to its great sensitivity in detecting lesions of the bone, it was therefore thought to exploit this characteristic to identify equally accurately inflammatory lesions of the skeleton or of the musculo-tendinous structures in the course of inflammatory rheumatic diseases.
In particular, the main advantages of total-body MRI in rheumatic diseases are essentially twofold
- it is possible to analyse, with a single examination, any inflammatory involvement of any site of the musculoskeletal system. In fact, total-body MRI allows a study of the body ‘in toto’, multi-organ, in a single examination.
- It combines the classic anatomical morphological data with functional data by exploiting the physical principle of diffusion. Diffusion is a modality of MRI that involves studying the molecular composition of individual tissues. Under normal conditions, molecules are free to move in tissue and cellular space, in which condition they do not generate any signal in certain sequences. Instead, it has been discovered that under pathological conditions (including the inflammatory conditions typical of rheumatic disease) the movement of molecules undergoes a ‘restriction’, creating a strong signal that is translated by MRI into images. Diffusion is therefore considered a functional analysis.
The whole-body diffusion MRI technique is a non-invasive method with an acquisition time of about 35-40 min, during which the patient must remain motionless.
There is no use of contrast media.
The images obtained, in coronal and sagittal planes, have an absolutely safe diagnostic content (MRI does not involve the use of hazardous ionising radiation).
It is possible to perform total-body MRI mainly under two conditions
- in the differential diagnosis of spondyloarthritis;
- in the diagnosis of myositis.
Spondyloarthritis is a large group of diseases with a common genetic substrate characterised, with varying frequency in the various types, by inflammatory involvement of the spine, peripheral joints and entheses (tendon insertions).
The best known are psoriatic arthritis and ankylosing spondylitis.
In a non-negligible percentage of cases, symptoms may be blurred and laboratory tests normal; in such situations, the differential diagnosis with non-inflammatory joint pathologies such as fibromylagia and osteoarthritis, and more generally with mechanical-postural pathologies, may be very difficult.
In such cases a total body MRI is certainly indicated, allowing a differential diagnosis with these conditions with high accuracy
Myositis, on the other hand, is a rather rare group of diseases that includes primary myositis, dermatomyositis, inclusion body myositis, necrotising myopathy and overlap syndromes with other autoimmune diseases.
They are all characterised by an inflammatory involvement of the skeletal musculature; clinically they lead to intense muscular asthenia, and on a laboratory level to increased blood values of muscle enzymes (cpk).
The most effective diagnostic test for the diagnosis is the muscle biopsy, which, however, cannot be performed in all patients and requires diagnostic centres equipped with specific expertise in the histological interpretation of the biopsy.
Precisely in such cases, MRI has a very high sensitivity in detecting inflammatory muscle lesions, so its total-body application is extremely useful in detecting the presence and location of possible myositis.
It also makes it possible to identify the muscle areas most affected and thus direct the point at which the muscle biopsy should be performed, thus considerably reducing the number of false negatives.
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