Mucocutaneous rash is the main external manifestation of syphilis. The causative agent of syphilis is the syphilis spirochete, which belongs to the genus Dense Spirochete in the family of small spirochetes. The pathogen of syphilis is also named as pale spirochete because of its transparent body fluid, smooth surface, and strong refractive power and not easy to stain. When syphilis damages the kidneys, patients with confirmed syphilis can be diagnosed with syphilis-related nephropathy if they also have abnormal urinary routine (proteinuria, hematuria), edema and renal function impairment, excluding primary renal disease and other secondary renal diseases. At this time, patients with mucocutaneous rash can have cerebrospinal fluid examination: 1. After pale spirochetes invade the central nervous system, the cerebrospinal fluid can be examined by checking the cell count, protein determination, spirochete examination, spirochete DNA, reactin test and specific antibody test. 2.If conditions permit, cerebrospinal fluid VDRL (CSF-VDRL) test, CSF-FTA-ABS test or CSF-TPHA test is feasible, and pallid spirochete DNA can also be examined. 3.Immunoblot test, 19s-IgM-FTA-ABS test, IgM-SPHA test, IgM-Captia test and CSF monoclonal IgM Antibody test, etc., all with high specificity. The test is indicated for early syphilis 1 year after anthelmintic treatment; syphilis of unknown stage or advanced syphilis; recurrent syphilis (either clinical or serologic); untreated syphilis of more than 2 years’ duration; all patients with latent syphilis.