Classic Appearance of Arthritic
Processes
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When an arthritic process is well established in a particular
patient, it will usually achieve a typical appearance, which allows diagnosis
by means of imaging.
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At such a moderately early or mid stage of disease, radiographs
are usually sufficient to make the correct diagnosis.
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The diagnosis usually depends on the location of the joint
abnormalities and a host of other radiographic characteristics.
Location of involved joints
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It can often eliminate some diagnoses and raise the probability
of others.
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For example, distal interphalangeal joint disease is commonly
seen in psoriatic arthritis, osteoarthritis, and erosive osteoarthritis.
However, it is not seen in rheumatoid arthritis until extremely late in the
disease; thus RA should not be considered in an early arthritis.
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Similarly, a disease involving the sacroiliac joints would raise
the possibility of ankylosing spondylitis, inflammatory bowel disease
arthritis, psoriatic spondyloarthropathy, chronic reactive arthritis,
osteoarthritis, and DISH.
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Note the joints that are involved earliest and most commonly are
distinguished from those involved less frequently or in end- stage disease.
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While the location of the joints involved certainly contributes
to establishing a list of reasonable diagnoses, the lists can be relatively
long, as in the examples above.
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There are several other parameters that are useful in honing
that list to a single diagnosis that are outlined in the tables that follow.
Further explanation regarding some of these parameters may be helpful.
Age and gender
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It may be the easiest parameters to apply.
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There are a minimal number of arthritic processes that affect children
(juvenile inflammatory arthritis, hemophilic arthropathy, inflammatory bowel
disease arthropathy, and septic joint) and teenagers (in addition to
those affecting children, early onset adult rheumatoid arthritis and ankylosing
spondylitis). Some diseases are gender specific (hemophilic arthropathy and
hemochromatosis), while others are found in one gender far more frequently
(gout, ankylosing spondylitis, chronic reactive arthritis in males, and
rheumatoid arthritis in females).
character of the process
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Erosive; rheumatoid arthritis is the hallmark for this
group.
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bone-forming (also termed "productive"). This bone formation may
appear in the form of osteophytes (as in osteoarthritis), enthesopathy or
ligamentous ossification (as in ankylosing spondylitis, DISH, and OPLL), or
periositis (as in psoriatic arthritis, chronic reactive arthritis, and juvenile
idiopathic arthritis).
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mixed, sometimes starting with erosions but
progressing to osteophytes (as in pyrophosphate arthropathy or gout) or
starting with periostitis and progressing to mixed erosions and osteophytes (as
in psoriatic arthritis or chronic reactive arthritis).
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These processes tend to be distinctive for each type of
arthritis by the time they are well established; between evaluating the
character of the process and its primary location in an individual, the
diagnosis can usually be secured.
Bilateral symmetry of an arthritic
process
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It can be a useful characteristic.
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Rheumatoid arthritis is especially well known for appearing
bilaterally symmetric. Note that rheumatologists do not require specific joints
of specific digits to qualify the arthritis as symmetric. For example, 5th PIP
left hand and 3rd PIP right hand would be considered symmetric disease simply
because of PIP involvement of each hand.
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Note also that bilateral symmetry may not be present in early
stages of arthritic disease, even in rheumatoid arthritis.
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Similarly, while we usually think of the sacroiliitis of
ankylosing spondylitis as being bilaterally symmetric, in its early stages the
symmetry is often strikingly absent.
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Therefore, useful generalizations regarding bilateral symmetry
are most often made in the mature stages of the disease process. However, rigid
application of "rules" of symmetry should be avoided when evaluating
early arthritis.
Soft tissue swelling
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It can be the key to finding the earliest changes of arthritis
on a radiograph.
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The sausage digit may lead to the discovery of subtle
periostitis, even in the absence of joint space narrowing or erosions.
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Swelling around a metacarpophalangeal joint may lead to closer
examination of a metacarpal head showing cortical indistinctness or the dotdash
pattern of early inflammatory disease.
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Be sure to window every image to evaluate the soft tissues, as
these abnormalities can lead to closer examination of adjacent joints.
Soft tissue masses
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They are not frequently seen in conjunction with arthritic
processes.However, they may lead to specificity in diagnosis.
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Gouty tophi, seen as a mass containing a variable degree
of dense tissue, can be diagnostic. As another example, soft tissue nodules,
combined with acroosteolysis and interphalangeal joint erosions, leads to the
rare diagnosis of multicentric reticulohistiocytosis. In differentiating
between the ligamentous ossification of DISH/OPLL, osteophytes of spondylosis
deformans, syndesmophytes of ankylosing spondylitis, and paravertebral
ossification of psoriatic arthritis and chronic reactive arthritis, the character of paravertebral
ossification can often suggest the
correct diagnosis. However, as with other parameters, it is important to note
that mature paravertebral ossification in each of these entities may all have a
similar appearance.
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True osteophytes may bridge across the disc space and give the
appearance of the flowing ligamentous ossification of DISH. Mature ankylosing
spondylitis has much bulkier syndesmophytes than the thin vertical ones
depicted in early disease.
Subchondral cysts
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They are seen in virtually all arthritic processes and therefore
are rarely useful in differentiating among them. However, occasionally the
subchondral cysts are so large that this characteristic becomes useful in
diagnosis.
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Particularly large subchondral cysts in a setting that otherwise
resembles rheumatoid arthritis lead to the diagnosis of robust rheumatoid
arthritis.
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Very large cysts are also noted in pyrophosphate arthropathy and
pigmented villonodular synovitis.
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Osteoarthritis and gout may also produce very large subchondral
cysts.
Bone density
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It must always be interpreted within the context of patient age
and gender.
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An elderly female will usually have diffuse osteoporosis, with
or without superimposed rheumatoid arthritis (classically described as causing juxtaarticular,
followed by diffuse osteoporosis).
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Thus, though we state that normal bone density is a
characteristic of osteoarthritis and gout, in an older patient those arthritic processes
may be seen in the presence of diffuse osteoporosis.
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Another example that may cause confusion is the young adult with
end-stage renal disease and a renal transplant.
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Erosive disease in these patients is likely to be gout or
amyloid. However, the bone density will be decreased due to both their renal
osteodystrophy and likely use of steroids for their transplant. In this case,
gout should be suggested to explain erosive disease, despite the bone appearing
osteoporotic.
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Focal osteoporosis
can also be helpful in identifying joints with active inflammation, as the
hyperemia from the inflammatory process leaches the calcium from the bone.
The pattern and timing of
cartilage destruction
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It may be another useful parameter.
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Some arthritides, such as gout, classically cause prominent
erosions before significant cartilage destruction, while most inflammatory
arthritides, such as rheumatoid arthritis, result in early marginal erosions but
also relatively early cartilage destruction.
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The pattern of cartilage destruction also distinguishes the
inflammatory arthropathies, where it is uniform throughout the joint as opposed
to the more focal cartilage destruction seen in the weight-bearing portions of
the joint in osteoarthritis.
Adjacent calcific or ossific
densities
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It may be particularly helpful in diagnosis.
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Chondrocalcinosis is not unique to pyrophosphate arthropathy but
is most frequently seen in that disease.
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The presence of chondrocalcinosis should also raise the question
of traumatic osteoarthritis and hemochromatosis.
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Calcifications in gouty tophi are usually unique in their
appearance.
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Calcific or ossific bodies in synovial chondromatosis are
different from the osseous debris seen with a Charcot joint. Therefore, the
character of adjacent calcific or osseous densities may be useful in the
diagnostic process.
Ankylosis of the peripheral joints
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is most commonly seen in psoriatic arthritis and juvenile idiopathic
arthritis.
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It is commonly found in the spine of patients suffering from spondyloarthropathies
(most frequently ankylosing spondylitis), DISH, and juvenile idiopathic
arthritis.
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Other more rare arthritic processes may show ankylosis as well.
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On the other hand, ankylosis in cases of rheumatoid arthritis is
exceedingly rare.
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Do not be fooled by a surgical arthrodesis in a patient with
severe rheumatoid arthritis. Arthrodesis is often attempted to stabilize the
digits in this disease, and may mimic ankylosis.
Early Appearance of Arthritic
Processes
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We are now diagnosing arthritic processes at an earlier stage, prior
to any radiographic change.
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This ability is essential, since early application of
disease-modifying drug therapy may halt joint destruction. The benefit of early
diagnosis is obvious, yielding longer patient productivity and decreasing the
need for arthroplasty. However, the diagnosis may be difficult with subtle or
absent radiographic findings and relies on MR or ultrasound.
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Early tenosynovitis and joint effusions may be identified on
ultrasound, and MR may demonstrate tenosynovitis, effusion, and bone marrow
edema long before actual erosions are seen in rheumatoid arthritis.
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Inflammatory change at vertebral body corners may be identified
on MR, indicating early spondyloarthropathy.
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Even more subtle may be the enthesitis and adjacent marrow edema
found in early ankylosing spondylitis, which are often found at the
"corners" of the image (interspinous ligaments, iliac spine, greater trochanter)
and are easily overlooked. Close attention should be paid to these locations,
even when evaluating a "routine lower back pain" spine MR exam.
Late Appearance of Arthritic
Processes
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End-stage arthritic processes may have a classic appearance.
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Classic changes are often seen in the deformities and erosive change
in rheumatoid patients or in the postural changes with vertebral column fusion
in ankylosing spondylitis patients. However, at times an arthritic process,
particularly when ineffectively treated, may attain a potentially confusing nonstandard
appearance. An example of this is the rheumatoid patient who has failed drug
therapy, resulting in an arthritis mutilans appearance of the hands (remember
that pencil-in-cup and arthritis mutilans are not exclusively seen in psoriatic
arthritis).
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Another example is the Native American ankylosing spondylitis
patient who is treated without the use of Western medications and may present
not only with the spondyloarthropathy expected in ankylosing spondylitis, but also
with erosive disease involving all the peripheral joints, including hands and
feet. Finally, the classic disease process that may be confusing is end-stage
gout, which, if misdiagnosed or undertreated, may result in spectacular erosive
disease at unexpected locations. It is important to remember that gout can look
like anything and can be located at any joint!
Coexistence of Arthritic Processes
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It is not unusual for two of the more common arthritic processes
to coexist, particularly in the elderly patient.
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This may be confusing initially but can be worked out through understanding
the prevalence of the diseases in the patient population, as well as by paying
attention to the appearance and location of the abnormalities present.
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The most common combination is a new onset of rheumatoid
arthritis superimposed on osteoarthritis.
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In this case, the osteoarthritis is usually well-established,
involving the 1st carpometacarpal and interphalangeal joints in classic
fashion, but there is new inflammatory change seen in the metacarpophalangeal
joints.
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The elderly patient may also develop pyrophosphate arthropathy,
superimposed over osteoarthritis or rheumatoid arthritis. The patient with a
diabetic Charcot joint may develop superimposed septic arthritis. Keeping these
possibilities in mind is useful to the interpreter, as the pattern of disease
may not be classic.
Image gallery
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Rheumatoid Arthritis distribution (common: Red; less common Yellow)
is shown. The hand is the hallmark of the disease, with distal radioulnar
joint, radiocarpal joint, intercarpal joint, MCP & PIP joint involvement.
Retrocalcaneal and 5th MTP involvement is most common in the foot, with other
ankle/hindfoot joints involved less commonly. Hip, knee, shoulder, elbow, temporomandibular,
and cervical involvement are common as well.
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Juvenile Rheumatoid Arthritis JIA distribution is shown. The knee, ankle,
and elbow are most frequently involved. In the hand, pericapitate and proximal
interphalangeal joints are most frequent, followed by radiocarpal, carpometacarpal,
and metacarpophalangeal joints. Cervical spine and temporomandibular involvement
are common, while the shoulder and hip are less so.
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