Forced Vital Capacity and Six-Minute Walk Test as Indicators of Interstitial Lung Disease Extent on High-Resolution Computed Tomography in Systemic Sclerosis

Variable	Extensive ILD (n=21)	Non-extensive ILD (n=62)	Total (n=83)	p
Age (years), mean (SD)	41.90 (10.07)	40.95 (11.16)	41.19 (10.84)	0.730
Sex — Male, n (%)	0 (0)	5 (8)	5 (6)	0.323
Sex — Female, n (%)	21 (100)	57 (92)	78 (94)	0.323
Smoking history — Non-smoker, n (%)	21 (100)	57 (92)	78 (94)	0.323
Smoking history — Moderate smoker*, n (%)	0 (0)	5 (8)	5 (6)	0.323
SSc subtype — Diffuse cutaneous (dcSSc), n (%)	13 (62)	42 (68)	55 (66)	0.709
SSc subtype — Limited cutaneous (lcSSc), n (%)	8 (38)	19 (31)	27 (33)	0.709
SSc subtype — Sine scleroderma (ssSSc), n (%)	0 (0)	1 (2)	1 (1)	0.709
Organ involvement — Musculoskeletal, n (%)	8 (38)	28 (45)	36 (43)	0.619
Organ involvement — Renal, n (%)	1 (5)	0 (0)	1 (1)	0.253
Organ involvement — Gastrointestinal, n (%)	10 (48)	14 (23)	24 (29)	0.049
mRSS, median (IQR)	8 (3–10)	7 (3–15)	7 (3–15)	0.459
Disease duration (months), median (IQR)	70 (12–114)	28 (10–90)	38 (11–95)	0.423
Predominant HRCT pattern — NSIP, n (%)	9 (43)	42 (68)	51 (61)	0.068
Predominant HRCT pattern — UIP, n (%)	12 (57)	20 (32)	32 (39)	0.068

ILD = interstitial lung disease; HRCT = high-resolution computed tomography; SD = standard deviation; IQR = interquartile range; mRSS = modified Rodnan Skin Score; SSc = systemic sclerosis; NSIP = non-specific interstitial pneumonia; UIP = usual interstitial pneumonia.

* Moderate smoker was defined as a Brinkman Index of 200–599 (cigarettes smoked per day × years of smoking). p-values: unpaired t-test (age); Mann-Whitney U test (mRSS, disease duration); chi-square test or Fisher's exact test as appropriate (categorical variables).

Table 2.

Functional, laboratory, and treatment characteristics of patients with systemic sclerosis according to ILD extent on HRCT.

Variable	Extensive ILD (n=21)	Non-extensive ILD (n=62)	Total (n=83)	p
6MWT distance (m), median (IQR)	330 (281–392)	349 (307–390)	348 (300–390)	0.492
Oxygen desaturation ≥4% during 6MWT, n (%)	3 (14)	0 (0)	3 (4)	0.015
FVC (% predicted), mean (SD)	47.0 (13.6)	64.7 (15.2)	60.2 (16.7)	0.001
FEV1/FVC (%), median (IQR)	90.5 (83–93)	87.8 (85–92)	88.4 (84–92)	0.480
ESR (mm/h), median (IQR)†	28 (12–59)	41 (27–62)	41 (25–61)	0.242
CRP (mg/L), median (IQR)‡	1.65 (0.77–5.42)	1.65 (0.77–6.72)	1.65 (0.77–6.07)	0.950
Anti-Scl-70 antibody, n (%)	4 (19)	12 (19)	16 (19)	1.000
Anti-centromere antibody, n (%)	0 (0)	3 (5)	3 (4)	0.568
Treatment — Treatmentnaïve, n (%)	1 (5)	7 (11)	8 (10)	0.423
Treatment — Methotrexate, n (%)	1 (5)	7 (11)	8 (10)	0.423
Treatment — Mycophenolate mofetil, n (%)	19 (90)	48 (77)	67 (81)	0.423

ILD = interstitial lung disease; HRCT = high-resolution computed tomography; SD = standard deviation; IQR = interquartile range; 6MWT = six-minute walk test; FVC = forced vital capacity; FEV1 = forced expiratory volume in 1 second; ESR = erythrocyte sedimentation rate; CRP = C-reactive protein.

† ESR available for 82/83 patients.

‡ CRP available for 78/83 patients.

Data on glucocorticoid and biologic agent use were not collected. p-values: unpaired t-test (FVC); Mann-Whitney U test (6MWT distance, FEV1/FVC, ESR, CRP); chi-square test or Fisher's exact test as appropriate (categorical variables).

Table 3.

Univariate association between functional parameters and ILD extent on HRCT.

Variable	Extensive ILD (n=21)	Non-extensive ILD (n=62)	PR (95% CI)	p
6MWT distance ≤338.35 m, n (%)	12 (57)	26 (42)	1.579 (0.743–3.353)	0.311
6MWT distance >338.35 m, n (%)	9 (43)	36 (58)	Reference	—
Oxygen desaturation ≥4%, n (%)	3 (14)	0 (0)	4.444 (2.95–6.69)	0.015
Oxygen desaturation <4%, n (%)	18 (86)	62 (100)	Reference	—
FVC <70% predicted, n (%)	21 (100)	38 (61)	1.553 (1.284–1.877)	<0.001
FVC ≥70% predicted, n (%)	0 (0)	24 (39)	Reference	—

[i] PR = prevalence ratio; CI = confidence interval; 6MWT = six-minute walk test; FVC = forced vital capacity; ILD = interstitial lung disease; HRCT = high-resolution computed tomography. p-values were calculated using Fisher’s exact test given the small expected cell counts.

Table 4.

Multivariable analysis of functional parameters associated with extensive ILD.

Variable	Crude PR (95% CI)	p	Adjusted PR (95% CI)*	p
FVC (% predicted)	0.952 (0.936–0.970)	<0.001	0.948 (0.931–0.965)	<0.001
Oxygen desaturation ≥4%	4.444 (2.959–6.675)	<0.001	4.333 (2.528–7.427)	<0.001
6MWT distance (m)	0.998 (0.995–1.002)	0.376	0.997 (0.993–1.002)	0.234

PR = prevalence ratio, estimated using Poisson regression with robust standard errors; CI = confidence interval; FVC = forced vital capacity; ILD = interstitial lung disease; mRSS = modified Rodnan Skin Score; 6MWT = six-minute walk test.

* Adjusted for age, disease duration, and mRSS. Age, disease duration, and mRSS were selected a priori as candidate confounders; none changed the crude PR by ≥10% (ΔPR), the pre-specified threshold for confounding.

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DOI: https://doi.org/10.2478/rjim-2026-0018 | Journal eISSN: 2501-062X (formerly 1220-4749) | Journal ISSN: 1220-4749

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Language: English, Romanian

Submitted on: Jun 15, 2026

Published on: Sep 7, 2026

Published by: N.G. Lupu Internal Medicine Foundation

In partnership with: Paradigm Publishing Services

Keywords:

systemic sclerosis,

interstitial lung disease,

forced vital capacity,

six-minute walk test,

high-resolution computed tomography

Related subjects:

Medicine,

Clinical medicine,

Internal medicine,

Internal medicine, other,

Cardiology,

Gastroenterology,

Rheumatology

© 2026 Sahat Halim, Cleopas Martin Rumende, RM Suryo Anggoro Kusumo Wibowo, Aulia Rizka, Gurmeet Singh, Mohamad Syahrir Azizi, Kaka Renaldi, Saut Horas Hatoguan Nababan, Kuntjoro Harimurti, published by N.G. Lupu Internal Medicine Foundation
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

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