The letter to the editor by Le Goff underlines the difficult differentiation of RS3PE from acute sarcoid arthritis and sarcoid periarthritis in patients with sarcoidosis. Indeed, all of these manifestations commonly affect the ankles and can present with erythema and tenderness of the lower leg(s), and pitting edema may be observed in patients with sarcoid periarthritis as well (1–3). Therefore, we fully agree with Le Goff that diagnosis of RS3PE in patients with sarcoidosis is a clinical challenge.
However, we strongly believe that we correctly diagnosed RS3PE in our patient for the following reasons: first, our patient presented with symmetric swelling of the ankles, pitting edema, and tenderness of the dorsum of the feet. It is unlikely that pitting edema of the dorsum of the feet occurs in a patient with pure (sarcoid) ankle arthritis. Second, red appearance of pitting edema, which was argued against the diagnosis of RS3PE by Le Goff, was also present in the case by Matsuda et al (4). Le Goff considered the case by Matsuda et al to be the only case of sarcoidosis that corresponds to the description by McCarty et al (5). Third, isolated manifestation of RS3PE at the lower extremities is not considered as an exclusion criterion for RS3PE (6, 7), although we agree that RS3PE of the hands was present in all patients in the article by McCarty et al (5). Fourth, young age and male sex are not exclusion criteria for RS3PE, although we concede that RS3PE is more common in elderly males. Fifth, ultrasound examination findings showed the combination of symmetric synovitis, tenosynovitis, and subcutaneous edema, which strongly supports the diagnosis of RS3PE (8–10). Inflammatory lesions in patients with sarcoid periarthritis are localized mainly in the subcutaneous tissue as shown by ultrasound studies, but do not include synovitis (11, 12).