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1 Institute of Diagnostic Radiology, University Hospital, Raemistrasse 100,
Zurich CH-8091, Switzerland.
2 Clinic of Rheumatology, University Hospital, Zurich, Switzerland.
Received March 18, 2004;
accepted after revision June 17, 2004.
Address correspondence to D. Weishaupt
(dominik.weishaupt{at}usz.ch).
Abstract
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MATERIALS AND METHODS. Six patients with histologically proven EF underwent MRI at the time of diagnosis and after therapy (15 MRI examinations). Unenhanced T1-weighted, T2-weighted, and STIR sequences were performed using a 1.5-T MRI system. In addition, all patients were imaged with contrast-enhanced T1-weighted sequences. MRI findings, clinical findings, and laboratory parameters were retrospectively reviewed.
RESULTS. At the time the six patients presented, all eight MRI examinations revealed symmetric thickening and hyperintensity of the superficial muscle fasciae of the thigh, calves, or arms on unenhanced T1-weighted, T2-weighted, or STIR sequences, with strong enhancement after administration of IV contrast agent. In seven of the eight MRI examinations, similar signal changes were also present in the deep muscle fasciae. After treatment, the fascial abnormalities found on MRI disappeared on six of eight MRI examinations performed in five patients—a rate that correlated well with the clinical findings. In one patient with EF involvement of the thigh, the MRI abnormalities showed partial remission, which also correlated well with the clinical findings.
CONCLUSION. In EF, MRI reveals characteristic findings including thickening, signal abnormalities, and contrast enhancement of the superficial and, to a lesser extent, deep muscle fasciae. MRI is useful for establishing the diagnosis, guiding the choice of biopsy site, and assessing treatment response.
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The cause and pathogenesis of EF are still unknown. EF may occur after strenuous exercise, and environmental exposure to various chemical substances and administration of simvastatin are also described as causative factors [8–12].
The diagnosis of EF is suspected on the basis of clinical and laboratory findings, but the definitive diagnosis can be established only by full-thickness skin-to-muscle biopsy [1, 2, 4–7, 13]. The contribution of MRI to the diagnosis of EF has been outlined by several case reports in the rheumatology and dermatology literature, as well as in the radiology literature [5, 6, 9, 13, 14]. However, to the best of our knowledge, in no large series have the MRI features of EF been described or the usefulness of MRI in monitoring EF been investigated.
The purpose of this study was to describe the MRI findings of EF in a series of patients with histologically proven EF and to correlate clinical and laboratory findings with MRI findings.
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The diagnosis of EF was based on a combination of clinical symptoms, laboratory findings, and histologic analysis. For all six patients, EF was pathologically proven by surgical full-thickness skin-to-muscle biopsy, including the fascia, after MRI.
For each patient, MRI was performed as part of the clinical routine during the diagnostic workup of the disease. MRI was also performed after therapy either when clinical remission and normalization of the patient's symptoms or laboratory parameters occurred or when no change or only minor improvement in clinical findings occurred after a 10-month trial with prednisone alone (15–70 mg/day orally) or in combination with methotrexate (15 mg/week subcutaneously). The combination of prednisone and methotrexate was given when inflammatory activity was judged high on the basis of clinical and laboratory findings. Follow-up MRI was performed between 12 and 40 weeks after treatment began (Table 1).
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MRI at both times (before and after therapy) and physical assessment of the patients (including laboratory analysis) were performed within 7 days for all patients. Before treatment, MRI was performed at the site at which the involvement was clinically suspected. After treatment, MRI was repeated at the same sites, except for one patient (patient 3) on whom MRI of the right forearm was performed only before treatment (Table 1). Overall, we performed 15 MRI examinations: pre- and posttherapy examination of both thighs of four patients, three examinations of the forearm of two patients (one whose left forearm was examined before and after therapy, and one whose right forearm was examined only before therapy), pre- and posttherapy examination of the right upper arm of one patient, and pre- and posttherapy examination of both calves of one patient (Table 1).
MRI
MRI was performed on a 1.5-T scanner (Signa Horizon, GE Healthcare) using a
multichannel phased-array peripheral coil (Medical Advances), except for upper
extremity (upper arm or forearm) examinations, which used a body coil, and
forearm examinations, which used a dedicated phased-array extremity coil with
the patient lying prone. The imaging protocol for all examinations included a
fast STIR sequence (TR/TE, 3,500–5,500/33; inversion time, 150 msec) in
the coronal or sagittal plane, an axial T1-weighted spin-echo sequence (TR/TE,
300–420/9–16), and an axial T2-weighted fat-suppressed fast
spin-echo (3,500/57–100; echo-train length, 8) or STIR
(3,500–5,500/33; inversion time, 150 msec) sequence. In addition, all
MRI examinations included acquisition of axial T1-weighted fat-suppressed
spin-echo images (300–540/9–16) after IV injection of 0.2 mmol of
gadolinium tetraazacyclododecantetraacetic acid (Dotarem, Labaratoire Guerbet)
per kilogram of body weight. Other imaging parameters included a field of view
of 48 x 36 cm for sequences in the coronal plane and 16–36 x
16–28 cm for sequences in the axial plane; an image matrix of 256
x 192–224; a slice thickness of 6–10 mm with an intersection
gap of 2–2.5 mm; and 2–4 acquisitions.
Data Analysis
Clinical data.—One author reviewed all clinical charts for
the clinical and laboratory findings at the time of diagnosis and during
treatment. The time between onset of symptoms and establishment of diagnosis
was recorded. In addition, one author noted whether the MRI findings
influenced the site of the skin-to-muscle biopsy. Treatment response was
classified as a complete remission if symptoms (e.g., pain) abated completely,
peripheral skin induration lessened significantly, and the eosinophilic count
of peripheral blood normalized (if peripheral eosinophilia had been present at
the time of diagnosis).
MR images.—All MR images were retrospectively analyzed in random order by one radiologist and one rheumatologist working independently. Consensus was obtained in cases of disagreement. Images were analyzed on a separate workstation (Advantage Windowing Workstation, GE Healthcare Europe). Neither observer was aware of the clinical findings or patient data or of whether therapy had been performed. The superficial and deep muscle fasciae were evaluated for the presence of fascial thickening, signal abnormalities or fascial enhancement, and fluid collections on T1-weighted, STIR, and T2-weighted fat-suppressed MR images and on contrast-enhanced T1-weighted fat-suppressed MR images. Both muscle and fascial signal abnormalities were compared with internal standards (a list of standard references at our institution) of skeletal muscle and fat on T1-weighted and STIR sequences. In addition, both observers noted skin and subcutaneous abnormalities. The superficial muscle fasciae at the different anatomic sites were defined as follows: upper arm, brachial fascia; forearm, antebrachial fascia; thigh, fascia lata; and calf, fascia cruris. The deep muscle fasciae were defined as the fasciae between the individual muscles. If abnormalities of the superficial or deep muscle fasciae were present, the anatomic distribution was noted. In addition, the muscles were evaluated for signal abnormalities and fluid collections, and the bone marrow was evaluated for abnormalities.
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At the time of first presentation at our institution, all six patients had skin thickening and induration of the involved extremities. In addition, hyperpigmented skin changes with a coarse orange-peel appearance were present in two patients and subcutaneous edema was present in one patient, with involvement of the calves. Three patients had limited flexion and extension of one or more joints, and synovitis was present in two patients.
Peripheral blood eosinophilia was present in five patients (1.5–2 times the upper limit). All six patients had a slightly or moderately elevated erythrocyte sedimentation rate (between 1.2 and 2 times the upper limit). The erythrocyte sedimentation rate was elevated (between 1.5 and 3 times the upper limit) in four patients, and C-reactive protein was elevated (between 1.5 and 3 times the upper limit) in five patients. In three patients, the total WBC was slightly elevated (between 1.1 and 1.4 times the upper limit). The antinuclear antibodies were slightly (1.2 and 2 times) elevated in two patients, and in one patient the rheumatic factor test results were elevated to twice the upper limit. Immunoglobulin levels were elevated in one patient. Creatinine phosphokinase and other blood chemistry levels were within reference limits in all patients.
MRI Findings at Time of Diagnosis
In all eight of the MRI studies that were performed at the time of
diagnosis (five MRI studies of both thighs, one of the upper arm, one of the
forearm, and one of both calves), thickening of the superficial muscle fasciae
was present on T1-weighted unenhanced MR images, with increased signal
intensity relative to the muscles on T2-weighted fat-suppressed or STIR images
(Figs. 1A,
1B, and
1C). After IV contrast
administration, enhancement was noted at all fascial sites at which signal
changes were present on unenhanced sequences. The fascial signal changes and
fascial contrast enhancement were symmetric in all patients for whom both
extremities were imaged at the same time. The signal hyperintensity on
T2-weighted or STIR sequences and the fascial enhancement were marked in six
MRI studies but less intense in the remaining two MRI studies, of both thighs
and calves (Figs. 2A and
2B).
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Changes similar to the fascial thickening, signal abnormalities, and contrast enhancement seen on T2-weighted and STIR images of the superficial muscle fasciae were also present in the deep muscle fasciae of seven of eight pretherapy MRI studies. In the thighs, the MRI abnormalities involved only the deep fasciae of the dorsally located muscles (extensors); the deep muscle fasciae of the ventrally located muscles were spared (Figs. 3A, 3B, 3C, and 3D).
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In three MRI examinations (two of the thigh and one of the forearm), signal hyperintensity on T2-weighted or STIR images, with slight contrast enhancement, was also present in muscle tissue adjacent to the muscle fascia (Fig. 4). No other abnormality was detected within the muscle fibers on the other MRI examinations. The cutis and subcutis showed no abnormalities, except for two studies (one of the upper arm and one of both calves) revealing a fine stranding with hyperintense signal changes in the subcutaneous tissue on fat-suppressed T2-weighted or STIR sequences. Because no definite contrast enhancement was present, these subcutaneous changes were interpreted as edema or panniculitis. In all other MRI examinations, no abnormality of the skin or subcutaneous tissue was noted. No subcutaneous, fascial, or other fluid collections were noted.
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The MRI findings determined the choice of biopsy site in all six patients. In all instances, a surgical full-thickness skin-to-muscle biopsy including dermis, fascia, and muscle tissue was performed. Histologic analysis of the specimens revealed foci of hyaline sclerosis, necrosis of the adipose tissue at the dermosubcutaneous junction, thick subcutaneous septa and fasciae, and a perivascular and interstitial infiltrate of lymphocytes, plasma cells, and, rarely, eosinophils (Fig. 5). No vasculitis was present in any biopsy specimen. Strands of sclerotic fibrous tissue consistent with panniculitis were noted in the one specimen in which subcutaneous signal abnormalities were detected on MRI.
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Clinical and MRI Findings During Follow-Up
Under therapy, complete remission was achieved in five patients. Comparison
of pretherapy and posttherapy MR images showed complete resolution of the MRI
signal changes of the superficial and deep muscle fasciae in six of the eight
MRI examinations of the five patients.
One patient treated with prednisone and methotrexate had a poor response to therapy. Typical features of EF in both thighs were seen on pretherapy MR images and showed only partial remission after therapy. The partial remission correlated well with clinical and laboratory findings, which showed a poor response to treatment in this patient (patient 3) after 40 weeks of therapy. No other abnormality was noted on posttherapy MR images.
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EF may occur at all ages, with the age at onset ranging from 2 to 73 years [13]. Women are more commonly affected than men [13]. In our series, EF was also more frequent in women than in men: Five of six patients were female, and only one was male. Patients' age at diagnosis was variable (age range, 32–76 years; mean, 57 years). The laboratory parameters at first presentation also varied considerably, and one patient did not have peripheral blood eosinophilia. The laboratory findings of our series showed no uniform constellation of serum laboratory or immunologic parameters for diagnosis of EF.
Because the clinical findings and laboratory parameters vary, the final diagnosis of EF can be established only by full-thickness skin-to-muscle biopsy. Although the use and imaging features of MRI for detection of EF have been described in several case reports [1, 4–7, 13], a full-thickness skin-to-muscle biopsy is still considered necessary for establishing the diagnosis. The results of our study, along with published data [1, 4–7, 13], clearly show that the MRI features of EF are characteristic and include thickening of the superficial and, less frequently, of the deeper muscle fasciae, with high signal intensity on T2-weighted or STIR sequences and strong fascial enhancement after IV administration of extracellular gadolinium-based contrast agents. These findings correspond to the microscopic histopathologic findings for the biopsy specimens in our study—findings that included fascial fibrosis with mixed cellular infiltration in all instances. We also observed that the typical MRI features of EF were present only in the dorsal deep fasciae of the thigh, whereas the muscle fasciae of the flexor group were not affected. Contrary to myositis and dermatomyositis, EF shows no or only minimal signal changes within the muscle fibers and only occasional MRI abnormalities in the skin and subcutaneous tissue. When the muscle fibers of patients with EF showed signal changes, they were present only near the fasciae. These signal abnormalities within muscle near inflamed fasciae probably represent an extension of inflammatory cellular infiltrate within the muscle, as may be observed histologically in EF [3]. The subcutaneous MRI signal abnormalities that were observed in the two instances in our study were caused by sclerotic fibrous tissue (panniculitis) in one patient.
Apart from being useful for establishing the diagnosis, MRI is also useful for choosing an adequate site for full-thickness skin-to-muscle biopsy. In all our patients, MRI findings guided the choice of skin-to-muscle biopsy site.
MRI findings associated with EF have to be differentiated clearly from those that may be seen in necrotizing fasciitis [17]. In the latter, MRI signal changes are usually not symmetric, and fascial thickening with contrast-enhanced muscular edema may be present [17]. In addition, MR images of necrotizing fasciitis frequently show fluid collections, abscess formation, and cellulitis.
No clear consensus exists on the treatment of EF. Only corticosteroids are unanimously considered an adequate treatment, but they may be ineffective, or they may be effective only at high doses (0.5 or 1 mg/kg per day) and thus bear the risk of many side effects. Benefits have been reported for treatment with methotrexate, cimetidine, penicillamine, and, more recently, cyclosporine [15, 18, 19]. The last two seem to be especially effective when corticosteroids are less effective or contraindicated.
Our study has also shown that MRI is highly useful for monitoring EF. The laboratory parameters under therapy were quite variable, similar to those at the beginning of the disease. In contrast, in all six patients MRI was useful for assessing therapy response.
We acknowledge several limitations of the study. It was retrospective, had no control group, included relatively few patients with EF, and did not evaluate the interobserver variability of the MRI findings.
In conclusion, our study has shown that in patients with EF, MRI reveals characteristic findings including thickening, signal abnormalities, and contrast enhancement of the superficial and, to a lesser extent, deep muscle fasciae. MRI is useful for establishing the diagnosis, guiding the choice of biopsy site, and assessing the response to therapy.
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