Background/Purpose Early diagnosis of interstitial lung disease (ILD), currently the main cause of death in systemic sclerosis (SSc), is needed. The gold standard is high resolution computed tomography (HRCT) of the chest, but regular screening faces the risk of increased radiation exposure. We perform a prospective validation of a dedicated, 9-slice HRCT protocol with reduced radiation dose for the detection of ILD in patients with SSc.

Methods We analysed 170/205 consecutive patients with SSc. Whole chest HRCT, serving as standard of reference, and the reduced HRCT with 9 slices allocated according to a basal-apical gradient were obtained. ILD presence, extent (>or<20%) and diagnostic confidence were assessed. The reduced CT was independently analysed by 2 blinded radiologists, who also evaluated image quality. The effective radiation doses and the test performance parameters of the reduced HRCT were calculated.

Results The study cohort included early (n=66), limited cutaneous SSc (n=66) and diffuse cutaneous SSc (n=34) patients, with a median disease duration of 60 months (Q1;Q3 28,120). Standard chest HRCT showed ILD in 77/170 patients. With the reduced HRCT, 68/77 cases with ILD were identified (sensitivity 88.3%, both readers). The accuracy (91.8%-reader1, 94.7%-reader2), diagnostic confidence (98.8%-reader1, 95.3%-reader2) and image quality rates were high (Table 1). Missed cases were exclusively borderline to minimal ILD on standard CT. Minimal ILD was correctly quantified in 73.1% (reader1) /71.2% (reader2) and extensive ILD in 88% (reader 1) /100% (reader 2) (Table 2). Importantly, the reduced CT had a significantly lower radiation dose. The mean DLP (effective dose) was only 5.66±4.46 mGycm (0.08±0.06 mSv), compared with the standard protocol dose of 149.00±95.90 mGycm (2.09±1.34 mSv).

The presence of associated lung pathology was also assessed. In this cohort, 8/10 lung nodules were also detected on the reduced CT (all <6 mm diameter and stable at follow-up).

Table 1.Estimated accuracy and diagnostic certainty in detecting ILD on reduced CT scans

	Reader 1	Reader 2
Sensitivity (95% CI)	88.3% (78.5%-94.2%)	88.3% (78.5%-94.2%)
Specificity  (95% CI)	94.6% (87.3%-98.0%)	100% (95.1%-100%)
Accuracy	91.8%	94.7%
NPV (95% CI)	90.7% (82.7%-95.4%)	91.2% (83.5%-95.6%)
High diagnostic   confidence*	98.8%	95.3%
* degree of confidence score 1 or 2 (i.e. 1 =   fully confident; 2 = probably confident); CI = Confidence interval (in   parenthesis), NPV = Negative predictive value

 

Table 2.Estimated extent of ILD in standard CT and reduced CT scans

Lung involvement in standard CT	Estimated extent in reduced CT
	No ILD	Minimal (<20%)	Extensive (>20%)	Indeterminate
	Reader 1/2	Reader 1/2	Reader 1/2	Reader 1/2
Minimal (<20%)    n = 52	n = 9/9	n = 38/37*	n = 5/6	n = 0/0
Extensive (>20%)  n = 25	n = 0/0	n = 3/0	n=22/25*	n = 0/0
ILD was present in 77 patients in standard CT. *Correctly estimated extent in reduced CT as  compared to standard CT.

Conclusion The above-described reduced chest HRCT protocol reliably detects even mild SSc-ILD in clinical practice, with the advantage of a much lower radiation dose compared to standard whole chest HRCT. This makes it an attractive protocol for periodical screening for ILD in SSc.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/screening-for-interstitial-lung-disease-in-systemic-sclerosis-performance-of-high-resolution-computed-tomography-with-limited-number-of-slices-a-prospective-study/