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1
Department of Radiology, Kaohsiung Veterans General Hospital, 386 Ta-Chung 1st
Rd. Kaohsiung, 813 Taiwan.
2
National Yang-Ming University, School of Medicine, 155, Sec 2, Li-Nong St.,
Shih-Pai Rd., PeiTou, Taipei, 112 Taiwan.
3
Department of Radiology, Veterans Affairs Medical Center and University of
California-San Diego, 3350 La Jolla Village Dr., San Diego, CA 92161.
Received July 12, 1999;
accepted after revision February 8, 2000.
Address correspondence to C. B. Chung.
Abstract
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MATERIALS AND METHODS. Retrospective review of the CT (n = 18) and MR imaging (n = 20) studies of the wrist in patients with a documented diagnosis of gout who presented with gout-related carpal tunnel syndrome was performed; images of 24 wrists were collected over a 5-year period. Patient population included 20 men, who ranged in age from 35 to 76 years. All images were reviewed by two musculoskeletal radiologists who reached a consensus opinion. Surgical correlation was available in 12 patients.
RESULTS. Tophi were found in the floor of the carpal tunnel (n = 18), carpal bones (n = 17), radiocarpal joint (n = 17), and extensor tendons or tendon sheaths (n = 16) of the wrist. All tophi showed similar signal characteristics (from low to intermediate signal intensity on T1-weighted images with heterogeneous signal intensity on T2-weighted images) with the exception of tophi in the floor of the carpal tunnel (low signal intensity on T2-weighted images). Varying degrees of calcification were noted on CT and MR imaging studies. Gadolinium-enhanced MR studies showed heterogeneous enhancement.
CONCLUSION. Gouty tophi should be entertained as a cause of carpal tunnel syndrome in the appropriate patient population. Familiarity with this entity and its imaging characteristics may prove helpful in diagnosis and preoperative planning.
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The patient population included 20 men, who ranged in age from 35 to 76 years old (mean age, 62 years). All patients presented with symptoms and signs of carpal tunnel syndrome including pain, paresthesias of the fingers in the distribution of the median nerve, or weakness and atrophy of the thenar muscles. The diagnosis of gout was supported by hyperuricemia in all patients at some point during their medical treatment. The mean serum urate concentration was 10.5 mg/dL for 18 patients at the time of the study; in the two remaining patients, serum urate level at the time of MR imaging was normal (paralleling recent treatment with uricosuric agents), but marked variability in this measurement had been documented in each patient's medical records, with levels as high as 13.8 mg/dL and 12.9 mg/dL before treatment. In addition, the identification of multiple gouty tophi or monosodium urate monohydrate crystals on polarized light microscopy in the analysis of aspirates from the wrist joint, tendon sheaths, or areas of soft-tissue swelling were present in five patients. Histologic evaluation including von Kossa's staining (for confirmation of calcification) of the biopsied specimen during carpal tunnel release was available in seven patients. The diagnosis of calcium pyrophosphate deposition disease or mixed crystal deposition disease (i.e., gout and calcium pyrophosphate dihydrate crystal deposition) was excluded by the absence of chondrocalcinosis on routine radiographs and by failure to identify positive birefringent crystals in the joint fluid (n = 11).
MR imaging was performed on a 1.5-T system (Signa; General Electric Medical Systems, Milwaukee, WI). A flexible volume coil or dual 3-inch (8-cm) phased array temporomandibular joint coils were applied. The patient lay prone with the wrist resting against the side in a prone or thumb-up position. Our protocol consisted of several sequences. A T1-weighted spin-echo sequence (TR range/TE range, 400-650/12-28) was performed in the coronal plane with a 3-mm section thickness, 0.3-mm intersection gap, 256 x 192 matrix, and 8-cm field of view; two signals were averaged. A T1-weighted spin-echo sequence (400-650/12-28) and a T2-weighted fast spin-echo sequence (TR range/effective TE range, 2800-6000/80-84; echo train length, eight) were performed with or without fat-suppression technique in the axial plane with a 3-mm section thickness, 1-mm intersection gap, 256 x 192 matrix, and 10-cm field of view; three signals were averaged. A sagittal T1-weighted spin-echo sequence (TR range/TE range, 400-650/12-28) was performed with a 4-mm section thickness, 0.5-mm intersection gap, 256 x 192 matrix, and 10-cm field of view; two signals were averaged. In addition, T2-weighted spin-echo or gradient-echo sequences in the coronal or sagittal plane were occasionally used. Gadolinium-enhanced MR imaging (400-650/12-28), using fat-suppressed T1-weighted spin-echo sequences in the axial and coronal planes, was also performed in nine wrists after IV administration of 0.1 mmol/kg gadopentetate dimeglumine (Magnevist; Schering, Berlin, Germany).
Contiguous 4-mm-thick axial CT images (Somatom HQ or Somatom Plus; Siemens, Erlangen, Germany) were obtained through the wrist joint. Images were displayed in both bone and soft-tissue windows.
The MR and CT images of each patient were reviewed together and simultaneously by two musculoskeletal radiologists who reached a consensus opinion. The extent, signal intensity (compared with that of muscle), and degree of gadolinium-enhancement of the tophi on MR images and the correlation of these findings with calcifications evident on CT images were recorded. An attempt to distinguish tophi from synovial proliferation was made based on the identification of the morphology of the abnormality (tophi usually being more focal), signal characteristics (tophi showing lower signal intensity on T2-weighted images), and associated regions of punctate low signal intensity suggesting calcifications within a tophus.
Surgical correlation was available in 12 patients, although specimen analysis was performed in only seven of these patients.
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Among the 20 standard MR imaging studies, the tophi were found in the floor
of carpal tunnel (i.e., the space between the flexor tendons and the carpal
bones) (18 wrists), in the carpal bones (17 wrists), in the radiocarpal joint
(17 wrists), in the flexor tendons or tendon sheaths (nine wrists), and in the
extensor tendons or tendon sheaths (16 wrists), especially the extensor carpi
ulnaris. All the tophi manifested low to intermediate signal intensity
compared with muscle, often containing small foci of very low signal intensity
on T1-weighted spin-echo images (Figs.
1A and
2C). On T2-weighted images, the
tophi showed variable signal intensities that ranged from low to high (Figs.
1B,
2B, and
3B) with the exception of tophi
in the floor of carpal tunnel, which had characteristic low signal intensity
in 17 of the 18 wrists (Figs.
1B and
3B). In the one exception,
high-signal-intensity tophi in the carpal tunnel floor on T2-weighted images
were associated with exuberant carpal bone lesions and synovitis of the wrist.
All the tophi in the carpal tunnel had variable degrees of calcification
visible on CT scans (Figs. 1D
and 3A). In addition, all
patients had at least three of the four following criteria for MR diagnosis of
carpal tunnel syndrome [16]:
swelling of the median nerve at the level of the pisiform bone (n =
15), flattening of the median nerve at the level of the hamate bone
(n = 14), palmar bowing of the flexor retinaculum at the level of the
hamate (n = 17), and abnormal signal intensity of the median nerve
(n = 14).
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Among the nine gadolinium-enhanced MR studies, moderate to marked degrees of enhancement were present in nearly all tophi (Figs. 1C, 2C, and 3C) except those in the carpal tunnel floor (Figs. 1C and 3C). A mild degree of heterogeneous enhancement of the tophi in the carpal tunnel floor was present in seven of the nine wrists. The remaining two wrists showed homogeneous enhancement associated with prominent enhancement of adjacent intraosseous lesions and synovium. Intraosseous cysts, manifesting characteristic fluid signal intensity and a thin enhancing rim, were not included in the assessment of tophi.
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Stippled calcifications were seen in all CT studies of 20 wrists in 15 patients (Figs. 1D and 3A). These calcified regions correlated with the small foci of very low signal intensity seen on T1-weighted MR images and with the diffuse stippled calcifications evident on histologic analysis with von Kossa's stain that was available in seven wrists. Among the 15 patients with calcific foci in the tophi, nine patients had mild impairment of renal function. The remaining six patients had normal renal function.
Twelve patients underwent carpal tunnel release. Analysis of tissue in the carpal tunnel was accomplished in seven patients. Under polarized light microscopy, needle-shaped crystals with strong negative birefringence were seen in all these surgical specimens. Calcification in the tophi was also confirmed using von Kossa's stain.
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Extensive calcifications, stippled or, less commonly, sheetlike in appearance, were present on all CT studies of wrists in our series. Calcified tophi in the wrist are reported to be rare [17, 18], and the presence of such calcification has been reported to suggest the possibility of coexisting calcium-containing crystals, an underlying abnormality of calcium metabolism (e.g., chronic renal disease), calcification within cholesterol deposited in the tophus, or extensive joint destruction with bone debris [18]. However, the occurrence of regions of high attenuation has been seen in cases of intraarticular tophi of the knee [19]. With regard to tophi in the knee joint, one report emphasized that these tophi are radiolucent on radiographs but are accompanied by higher attenuation values than soft tissue on CT scans [19]. In this study, the increased attenuation of these intraarticular tophi was considered to be related to a high concentration of sodium nuclei in the monosodium urate crystals. Conversely, however, in our study, the cause of increased attenuation as seen on CT examination appeared to be actual calcification within the tophaceous deposits, although this finding was confirmed by biopsy and analysis in only seven cases.
The MR imaging characteristics of gout have been described previously, mainly in case reports [20,21,22,23,24]. In these reports, gouty tophi have appeared as regions of signal intensity on T1-weighted images that are homogeneous and generally isointense to muscle [20]. The results with regard to T2-weighted images have been more variable. On these images, gouty tophi may have homogeneous high signal intensity [20, 25] or low signal intensity [22,23,24]. The most commonly reported signal intensity characteristic of tophi on T2-weighted images has been heterogeneous deposits. With regard to these previous reports, the hyperintense signal intensity that has been seen on T2-weighted spin-echo images may reflect the high protein content in the amorphous center of the tophus [24], whereas the decreased signal intensity on these images may indicate regions of calcification within the tophus [20], fibrous tissue and crystals [22], hemosiderin deposition, or proton immobility [23]. Our findings are consistent with those previously reported in the literature with the exception of the tophi located in the floor of the carpal tunnel.
With regard to IV gadolinium administration, reported patterns of enhancement have been inconsistent, with some descriptions indicating homogeneous and intense enhancement and others indicating heterogeneous and peripheral enhancement [20,21,22,23]. Furthermore, proliferative synovitis, which occurs in gouty synovitis, may be accompanied by enhancement of a tophus, reflecting hypervascularity of the affected synovium [20]. In our study, the tophi in the floor of carpal tunnel generally showed the following characteristics: low signal intensity on both T1-and T2-weighted images with only minimal heterogeneous enhancement after IV gadolinium administration. This finding is similar to our observations regarding the appearance of the intraarticular tophi in the intercondylar notch of the knees [1].
Although conservative medical treatment may be effective [6, 26], most previous reports have recommended surgical decompression of the carpal canal (division of transverse carpal ligament, with or without debulking of the tophi, tenosynovectomy, or both) whenever there is symptomatic median nerve compression [6, 7, 9, 10]. Postoperatively, poor healing, dehiscence of the surgical wounds, discharge of tophaceous material, and precipitation of an acute gouty attack [3, 27] may be evident, and these complications can be prevented by perioperative medications [3, 7, 8, 13]. In our series, persistent or recurrent carpal tunnel syndrome was present in three wrists.
Carpal tunnel compression may be the first manifestation of gout [7]. Of the two examinations, MR imaging best defined the extent and location of the tophi. CT, however, was advantageous with regard to detection of characteristic calcifications in the tophi.
The weaknesses of this study include a selection bias imposed because of its retrospective nature and the selection criterion of a history of documented gout. All the patients in the study population are male, with a mean age of 62 years. The study can only allude to the likelihood that this entity is more common than previously suggested by scattered case reports in the literature because no data regarding the total number of wrist MR imaging studies or CT scans obtained for carpal tunnel symptoms during the study period are available to provide a more exact reflection of incidence in our patient population. Finally, surgical specimen analysis was available in only seven cases and was not directed to tophi in the carpal tunnel floor, which showed unique imaging characteristics compared with the other regions.
In conclusion, despite the fact that gouty tophi have been a recognized but rare cause of carpal tunnel syndrome in the literature, this series of 20 patients suggests that this diagnosis should be entertained in the appropriate patient population. Moreover, preoperative investigation with regard to the presence, location, and complexity of gouty lesions may be beneficial in patients with carpal tunnel syndrome for surgical planning and appears to be best achieved using MR imaging. Gouty deposits in the carpal tunnel have signal characteristics similar to those found elsewhere in the body with the role of gadolinium remaining questionable because of associated findings of synovitis and minimal heterogeneous enhancement of tophi in our patient population.
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