Tc-DTPA clearance and rheumatoid arthritis-associated fibrosing alveolitis

V. V. Kaushik, M. P. Lynch and J. K. Dawson

Department of Rheumatology, St Helens Hospital, Marshalls Cross Road, St Helens, Merseyside, UK

SIR, The recent article by Rajasekaran et al. [1] incorporates the use of inhaled technetium-labelled diethylenetriamine pentaacetate (Tc-DTPA) clearance in the assessment of rheumatoid arthritis (RA) patients with interstitial lung disease (ILD). This technique has a potential role in indicating the presence of ILD and identifying stable ILD. However, the authors mention that this technique has not been studied previously in RA.

Tc-DTPA clearance was incorporated in an excellent study of ILD in early RA by Gabbay et al. [2], who assessed 36 patients with early RA by exercise testing, full pulmonary function tests, thoracic high-resolution computed tomography (HRCT), Tc-DTPA clearance and bronchoalveolar lavage. Thirty-three per cent of the patients had changes compatible with ILD on HRCT and 15% had abnormally rapid Tc-DTPA clearance. After all the investigations, 14% were found to have clinically significant ILD. On statistical analysis, no association was found between rapid Tc-DTPA clearance and clinically significant ILD.

We studied the use of Tc-DTPA clearance in the pulmonary assessment of 90 hospital out-patients with RA. All patients underwent clinical assessment, chest radiography, full pulmonary function tests, measurement of Tc-DTPA clearance and thoracic HRCT. Tc-DTPA clearance was measured only in non-smoking patients with RA because of the well-recognized association between smoking and rapid Tc-DTPA clearance [3]. Another aspect that differed from the study by Rajasekaran et al. [1] is that we used 40 min as the clearance half-life cut-off, which is the value stated in the Methods section of Wells et al. [4]. We found 27 patients with rapid Tc-DTPA clearance. Of these, seven had changes consistent with a reticular pattern of fibrosing alveolitis (FA) on HRCT. Rapid Tc-DTPA clearance was significantly associated with FA on HRCT (P=0.048). In non-smokers, rapid Tc-DTPA clearance had a sensitivity of 54% and a specificity of 74% in predicting FA on HRCT.

A major problem we found was central airway deposition of Tc-DTPA in patients with chronic obstructive pulmonary disease; not all of this could be predicted from pulmonary function tests. Central airway deposition of Tc-DTPA normalizes clearance time, because the bronchial surfaces have been shown to absorb Tc-DTPA more slowly than the alveolar epithelium [5]. Seventeen patients demonstrated obstructive patterns in their pulmonary function tests. When these patients were excluded, the univariate analysis showed an improved association of rapid clearance of Tc-DTPA with FA (P=0.019) and an improvement in sensitivity to 64% in predicting FA on HRCT. However, two patients who had both FA and obstructive lung disease were excluded.

We found in one patient, who died rapidly from RA-associated FA, that central deposition of isotope again resulted in a normal clearance time. This is an important issue as this normal clearance in a patient with rapidly progressive ILD is in contrast to the work of Wells et al. [4]. Wells et al. found deterioration in none of 23 patients who had FA and normal Tc-DTPA clearance.

Hence, we feel that if Tc-DTPA clearance has a useful role in RA-associated FA it is likely to be demonstrated in patients who have never smoked.

Notes

Correspondence to: J. K. Dawson. Back

Accepted 28 December 2001

References

  1. Rajasekaran BA, Shovlin D, Lord P, Kelly CA. Interstitial lung disease in patients with rheumatoid arthritis: a comparison with cryptogenic fibrosing alveolitis. Rheumatology2001;40:1022–5.[Abstract/Free Full Text]
  2. Gabbay E, Tarala R, Will R et al. Interstitial lung disease in recent onset rheumatoid arthritis. Am J Respir Crit Care Med1997;156:528–35.[Abstract/Free Full Text]
  3. Jones GJ, Royston D, Minty BD. The physiology of leaky lungs. Br J Anaesthesia1982;54:705–21.[ISI][Medline]
  4. Wells AU, Hansell DM, Harrison NK, Lawrence R, Black CM, du Bois RM. Clearance of inhaled 99mTc-DTPA predicts the clinical course of fibrosing alveolitis. Eur Respir J1993; 6:797–802.[Abstract]
  5. Kanazawa M, Suzuki Y, Ishizaka A et al. Assessment of pulmonary aerosol deposition and epithelial permeability in 99mTc-DTPA inhalation scintigram. Nihon Kyobu Shikkan Gakkai Zasshi1993;31:593–600.[Medline]

 

Reply

C. A. Kelly, V. Saravanan, D. Shovlin and B. A. Rajasekaran

Department of Rheumatology, Queen Elizabeth Hospital, Gateshead Health NHS, Sheriff Hill, Tyne & Wear, Gateshead NE9 6SX, UK

SIR, Drs Kaushik, Lynch and Dawson raise an interesting debate about the potential value of technetium clearance in the assessment of interstitial lung disease in patients with rheumatoid arthritis. We are grateful to them for pointing out that the work of Gabbay et al., in which 12 patients had early interstitial lung disease and five had accelerated technetium clearance, no correlation between these findings was found. These results were similar to ours.

By contrast, Kaushik et al. did demonstrate an association between rapid technetium clearance and interstitial lung disease in non-smokers, with reasonable sensitivities and specificities. Whilst their exclusion of smokers from the correlation may have accounted for the difference between their findings and those of others, there remain some practical difficulties. First, the frequency of significant airway obstruction in rheumatoid arthritis is such that it can lead to false-negative scans in a significant proportion of patients. Furthermore, smoking itself is associated with rheumatoid arthritis and the majority of patients are either active or ex-smokers, so exclusion of these patients means that technetium clearance can only be relied upon in a minority of subjects.

It appears that the potential value for technetium clearance scanning in interstitial lung disease is diluted in rheumatoid arthritis by the high prevelance of both smoking and airway obstruction.

Notes

Correspondence to: C. A. Kelly. Back

Accepted 28 December 2001





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