The last two decades have witnessed the explosion of new imaging modalities used to diagnose and evaluate the musculoskeletal disorders. In particular, the constant improvements of computed tomography (CT) with its newest spiral (helical) and three-dimensional (3D) variants, multichannel multidetector row CT (MDCT), dual-energy CT (DECT), high resolution flat-panel volume CT (fpVCT), dynamic 4D CT of the joints, and 3D CT angiography, as well as magnetic resonance imaging (MRI) with its 3D variant, delayed gadolinium-enhanced MRI of cartilage (d-GEMRIC), sodium (23Na) MRI of cartilage, 3D MRI/CT fusion imaging, MRI diffusion tensor imaging (MRDTI), and PET-MRI among the others, created a great deal of confusion in the proper use of these techniques in the circles of not only referring physicians/rheumatologists, but also radiologists (Fig. 1). The question “what to order” and “in what order” became crucial not only from the standpoint of the cost of medical care, but also from vantage point of the patient, who commonly is subjected to too many, and frequently unnecessary imaging tests. The diagnosis of many rheumatologic disorders can be made solely on the basis of particular recognizable radiographic pattern, whether it is a characteristic radiographic morphology of the articular lesion, or the characteristic distribution of the lesion in the skeleton and in the particular anatomic site such as the hand. These radiographic findings coupled with thorough clinical examination and laboratory results can lead to the correct diagnosis without using more advanced imaging modalities such as CT or MRI.
Fig. 1.
The choice of most effective imaging technique for particular rheumatologic abnormality will greatly benefit the patient
From the clinical point of view for example, the various arthritides have different frequencies of occurrence between the genders. Rheumatoid arthritis is much more common in females, whereas psoriatic arthritis, reactive arthritis, and gouty arthritis are more common in males. Erosive osteoarthritis is seen almost exclusively in middle-aged woman, and hemochromatosis arthropathy affects men ten times more frequently than women. Clinical symptoms are also of utmost importance. For instance, patients with reactive arthritis usually present with urethritis, conjunctivitis, and mucocutaneous lesions, those with psoriatic arthritis may present with a swelling of a single digit (so-called “sausage-digit”), as well as changes in the nails and skin, and gouty arthritis may present in some patients as a “podagra”, affecting the great toe. Those patients, in addition, may develop soft tissue masses, usually on the dorsal aspect of the hands and feet, representing gouty tophi. Patients with inflammatory arthritis, such as rheumatoid, commonly exhibit swelling of the joints and misalignment deformities. Flexible contractions and subluxations of the digits of the hands are characteristic for systemic lupus erythematosus arthropathy.
Laboratory data are also essential. Gouty arthritis, for example, is associated with elevation of the serum uric acid concentration, and examination of synovial fluid reveals monosodium urate crystals. The synovial fluid of patients with calcium pyrophosphate dihydrate (CPPD) crystal deposition disease contains calcium pyrophosphate crystals. Equally important is determination of C-reactive proteins (CRP), anti-cyclic citrullinated peptides antibodies (anti-CCP Ab), antineutrophil cytoplasmic antibodies (ANCA), cryoglobulins, antinuclear antibodies (ANA), anti-dsDNA antibodies, anti-RNP antibodies, and rheumatoid factor (RF). Lastly, identification of the antigens of the major histocompatibility complex, particularly human leukocyte-associated antigens HLA-B27 and HLA-DR4 has in recent years become the crucial tests in diagnosis of rheumatologic disorders.
Radiographic features of some arthritic disorders are characteristic for that particular disease. In osteoarthritis, thinning of articular cartilage results in narrowing of the radiographic joint space; there is subchondral sclerosis, degenerative cysts and osteophyte formation, but generally osteoporosis is absent. In the hands, classic Heberden and Bouchard nodes are characteristic for this arthrosis. Central erosions and peripheral proliferation of bone assuming the so-called gull-wing configuration characterize erosive osteoarthritis. Inflammatory arthritides, such as rheumatoid arthritis, are characterized by a diffuse, usually multicompartmental joint space narrowing, associated with central or marginal erosions, periarticular osteoporosis, and symmetric periarticular soft tissue swelling. Subchondral sclerosis is absent or minimal, and there is a lack of osteophyte formation. Psoriatic arthritis affecting distal interphalangeal joints of the hands and feet commonly exhibits characteristic erosion associated with fluffy periostitis termed “mouse-ear” appearance. Gouty arthropathy is characterized by well-defined osseous (articular or paraarticular) erosions, commonly asymmetric in location, displaying the so-called overhanging edge, associated with preservation of part of the joint, and accompanied by various in size dense soft tissue masses (tophi). Infection arthritis is characterized by complete destruction of both articular ends of bone forming a joint; all communicating joint compartments are invariably involved, associated with diffuse osteoporosis, soft tissue swelling, and joint effusion. Neuropathic arthropathy is marked by destruction of articular surfaces, joint debris, and substantial joint effusion. Osteoporosis usually is lacking or minimal, and there is a variable degree of joint instability.
Analysis of the morphologic features of an arthritic lesion at certain sites other than the diarthrodial joints may be of further assistance in differential diagnosis of arthritis. In the heel, rheumatoid arthritis produces erosive changes of the calcaneus at the site of retrocalcaneal bursa secondary to inflammatory rheumatoid bursitis. Psoriatic arthritis, reactive arthritis, and ankylosing spondylitis all produce characteristic fluffy periostitis that results in a broad-based osteophyte at the insertion of fascia plantaris on the plantar aspect of calcaneus, associated with erosions of this bone. In the cervical spine, rheumatoid arthritis causes characteristic erosion of the odontoid process, which together with inflammatory pannus destroying the transverse ligament between the anterior arch of the atlas and C2, results in C1-C2 instability effectively demonstrated on the flexion view of the cervical spine. Erosions of the apophyseal joints of the cervical spine, occasionally leading to fusion, are commonly seen in juvenile idiopathic arthritis. In the early stages of ankylosing spondylitis there is characteristic squaring of the vertebral bodies associated with so-called “shiny corners” or Romanus lesion, representing small erosions surrounded by reactive sclerosis and bone proliferation at the corners of the vertebral bodies at the attachment of the annulus fibrosus to the vertebral end-plate. This follows the formation of delicate syndesmophytes arising from the anterior aspect of the vertebral bodies. In the later stages of ankylosing spondylitis, inflammation and fusion of the apophyseal joints and calcification of the anterior and posterior longitudinal ligaments leads to so-called “bamboo spine”, very characteristic for this disorder. The sacroiliac joints are invariably affected (symmetric sacroiliitis). In psoriasis and reactive arthritis another characteristic feature may help to confirm the diagnosis, namely the presence of a single coarse osteophyte/syndesmophyte in the lumbar spine, commonly bridging the adjacent vertebral bodies, and formation of paravertebral ossifications.
Distribution of the articular lesions in the hand varies with type of arthritis. Osteoarthritis and erosive arthritis invariably affect the proximal and distal interphalangeal joints. The distal interphalangeal joints are usually spared in rheumatoid arthritis, which tends to affect primarily metacarpophalangeal and proximal interphalangeal joints. Conversely, psoriatic arthritis has predilection to the distal interphalangeal joints. CPPD crystal deposition disease and hemochromatosis arthropathy typically affects the metacarpophalangeal articulations, commonly associated with chondrocalcinosis.
As one can see from the above-provided discussion, there are numerous clinical, laboratory, and radiographic findings extremely helpful in making the correct diagnosis of a specific arthritis. We can confidently make a “step back to the future” and embrace again the conventional radiography as a very reliable imaging technique (Fig. 2). Making this statement, I am not completely disregarding MRI, which is extremely helpful, perhaps not so much as a diagnostic tool in rheumatology, but as a modality that can detect the inflammatory process much earlier than any other techniques, thus allowing to start an early treatment, so crucial in managing the rheumatologic diseases. The same can be said about dual-energy CT, the technique that in not so obvious cases is able to pinpoint the location of monosodium urate mineralization, thus confirming the presence of gouty arthropathy. But let us not be so overanxious in reaching to those advanced imaging modalities before we thoroughly explored the more simple imaging techniques! Conventional radiography is a wonderful tool in the hands of a prudent radiologist and should be appreciated by those rheumatologists who keep in mind the cost of management and the wellbeing of their patients.
Fig. 2.
Conventional radiography should always be the first imaging technique to evaluate accurately the joint pathology