Background The modified Rodnan skin score (mRSS) detects both severity and extension of skin involvement. High frequency skin ultrasound (US) can measure dermal thickness (DT) in patients with systemic sclerosis (SSc) (1-2).
Objectives To compare the values of DT obtained by two different ultrasound transducers (18 MHz and 22 MHz) in evaluating the DT in SSc patients and healthy controls.
Methods Forty-eight SSc patients (EULAR 2013 criteria) (mean age 64±11SD years, mean disease duration 6±5 years) and 20 healthy subjects (mean age 66±14 years) were enrolled, after informed consent (3). Two US transducers (Esaote, Genoa, Italy) with different frequency (18 and 22 MHz) were simultaneously used to measure DT in the areas of the skin always evaluated by mRSS (cheeks, fingers, dorsum of hands, forearms, arms, chest, abdomen, thighs, legs, feet). Stored images were subsequently analysed to calculate the DT, always by the same operator (BR). Statistical analysis was carried out by non parametric tests.
Results DT evaluated with the 22 MHz probe was found significantly higher in all body areas in comparison with the 18 MHz transducer, both in SSc patients (median millimetres 0.90 vs 0.88 for cheeks,1.32 vs 0.88 for right finger, 1.32 vs 0.93 for left finger, 0.97 vs 0.85 for dorsum of right hand, 0.97 vs 0.85 for dorsum of left hand, 1.10 vs 1.00 vs for right forearm, 1.05 vs 1.00 vs for left forearm, 1.20 vs 1.10 for right arm, 1.15 vs 1.10 for left arm, 1.31 vs 1.30 for chest, 1.40 vs 1.30 for abdomen, 1.40 vs 1.30 for right thigh, 1.40 vs 1.20 for left thigh, 1.10 vs 1.00 for right leg, 1.10 vs 1.09 for left leg, 0.99 vs 0.98 for right foot, 0.99 vs 0.98 for left foot, respectively) (p<0.01) and in healthy subjects (median millimetres 0.69 vs 0.68 for cheeks, 0.70 vs 0.69 for right finger, 0.71 vs 0.70 for left finger, 0.70 vs 0.68 for dorsum of right hand, 0.70 vs 0.69 for dorsum of left hand, 0.77 vs 0.76 vs for right forearm, 0.77 vs 0.76 vs for left forearm, 0.86 vs 0.85 for right arm, 0.86 vs 0.85 for left arm, 1.13 vs 1.12 for chest, 1.13 vs 1.12 for abdomen, 1.10 vs 1.07 for right thigh, 1.10 vs 1.09 for left thigh, 0.94 vs 0.93 for right leg, 0.94 vs 0.93 for left leg, 0.89 vs 0.86 for right foot, 0.90 vs 0.89 for left foot, respectively) (p=0.05). The median difference of DT values between the two probes was of 0.11 millimetres in SSc patients (minimum 0.0023, maximum 0.28 mm) and 0.01 millimetres in healthy subjects (minimum 0.0029, maximum 0.03 mm). A positive statistically significant correlation was observed between the two transducers (18 and 22 MHz) in the evaluation of DT (r=0.92, p<0.0001), as well as between both probes and mRSS (r=0.56, p<0.0001 for both).
Conclusions This study confirms that DT can be well detected in SSc patients by high frequency US (22 MHz), but suggests that DT might be underestimated by using US probes of lower frequency (18 MHz). However, the DT values obtained using both probes resulted significantly correlated together and with the mRSS.
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Disclosure of Interest None declared