This article reports the diagnosis and treatment course of a patient with granulomatosis with polyangiitis (GPA) complicated with Kennedy disease (KD). The patient presented with headache, purulent and bloody rhinorrhea, ocular pain, decreased hearing and vision, multiple nodular erythema with ulcers on both lower extremities, and lower limb weakness. Chest imaging revealed a nodule with cavity formation in the right lung, and cytoplasmic anti-neutrophil cytoplasmic antibody (c-ANCA) and proteinase 3-antineutrophil cytoplasmic antibody (PR3-ANCA) were positive. The patient was initially diagnosed with granulomatosis with polyangiitis. After treatment with glucocorticoids and cyclophosphamide, the vasculitis-related symptoms were relieved while lower limb weakness got worse. Genetic testing identified 50 CAG repeats in exon 1 of the androgen receptor (AR) gene, and the final diagnosis was GPA complicated with KD. After rehabilitation therapy, the patient′s lower limb weakness improved. Methylprednisolone combined with leflunomide was administered for maintenance treatment, and the condition remained stable during long-term follow-up.