Two years ago, a female patient in her early 20s had visited several large hospitals in our city for recurrent limb weakness for 5 years, which was diagnosed as polymyositis and was given long-term glucocorticoid treatment, but her symptoms did not significantly relieve. With the attitude of giving it a try, the patient came to my specialized outpatient clinic for treatment. Due to the long-term disease problems and poor treatment results, this patient lost confidence in her future and life. The first thing she said to me was, “Doctor, can I still be cured of this disease? How much longer do I have to use hormones?” While I reassured the patient to build up her confidence in treatment, I systematically conducted medical history questioning, physical examination, and reviewed the results of ancillary tests. After a series of comparisons, I became suspicious of the patient’s previous diagnosis, so I next admitted the patient and re-examined her muscle biopsy. The results of the histological and enzymatic staining examination did not support the diagnosis of polymyositis, but rather a rare metabolic myopathy called lipid deposition myopathy. Thereafter, on the one hand, blood and urine organic acid tests and genetic tests were contacted, and on the other hand, the treatment plan was immediately adjusted with vitamin B2 level and levocanidine, etc. Half a month later, the patient’s weakness was significantly reduced. 2 months later, the results of genetic tests also confirmed that it was a lipid deposition disease associated with vitamin B2 deficiency. 3 months later, at follow-up, the patient basically recovered completely and the ” At the follow-up visit after 3 months, the patient had basically recovered completely, and the “full-moon face” had disappeared, finally revealing a long-lost smile.