Objective: The purpose of this study is to report a case of adolescent-onset rheumatoid arthritis presenting with severe pain in the knee, wrist, and plantar region, which was diagnosed with Lesser yin disease provision number 315 and treated with Baektong-tang (白通湯) based on the Shanghanlun Disease Pattern Identification System (辨病診斷體系). This report aims to explore the applicability of Lesser yin disease patterns and Baektong-tang to autoimmune inflammatory joint disease associated with overwork and constitutional exhaustion. Methods: The diagnostic process and prescription were conducted according to the Shanghanlun Disease Pattern Identification System, focusing on the Lesser yin disease category and the classical clause "少陰病 下利 脉微者 與白通湯". Clinical data were collected through structured medical interviews, physical examination, and follow-up assessments of joint pain, daily activity level, and general fatigue during a 45-day treatment period. Results: Baektong-tang (Allii Fistulosi Bulbus, Zingiberis Rhizoma, Aconiti Lateralis Preparata Radix) was administered for 45 days with good medication adherence and no adverse effects. Within 15 days, overall joint pain decreased from severe to moderate levels, and by 30 days the patient reported minimal pain, resumption of drum playing, and improved exercise capacity. At 45 days, daily function was largely restored, and the patient was able to enjoy social and musical activities without significant discomfort. Conclusions: This case suggests that Baektong-tang, a representative formula for Lesser yin diseasee with depletion and cold, can be applied to adolescent-onset rheumatoid arthritis accompanied by overwork, sleep deprivation, and constitutional hypersensitivity, when interpreted through the Shanghanlun Disease Pattern Identification System. Further prospective studies are needed to clarify the indications and mechanisms of Baektong-tang in autoimmune rheumatic diseases.