Weighed against the AAV alone group, there have been more women, with an increased frequency of venous thrombotic events, and an increased price of non-renal relapse in the AAV overlapping CTD group [10]. and hemodialysis. After treatment, his clinical symptoms remained stable, and his creatinine and C-reactive protein (CRP) levels have remained normalized as of his most recent follow-up after hospital discharge. == Conclusions == AAV can overlap with SSc; although this condition is rare, it is usually associated with considerable morbidity and mortality. Therefore, it is critical to identify AAV in the setting of worsening renal function due to SSs and provide appropriate treatment. Several clinical features are suggestive of AAV rather than SRC, but renal biopsy is required for accurate diagnosis. Keywords:Systemic sclerosis, Vasculitis, ANCA, ANCA-associated vasculitis == Background == Systemic sclerosis (SSc) is usually a chronic autoimmune disease characterized by progressive thickening of the skin and fibrosing of multiple organs, including the heart, lungs, kidneys, and gastrointestinal tract. The prevalence of SSc ranges from 7 to 489 cases per million populace, and its incidence ranges from 0.6 to 122 cases per million populace annually [1]. SSc cases are categorized 17-AAG (KOS953) as either limited cutaneous SSc 17-AAG (KOS953) (lcSSc) or diffuse cutaneous SSc (dcSSc) based on the extent of skin involvement [1,2]. Even though pathogenesis of SSc is not completely comprehended, it is believed that deregulated production of autoantibodies and cytokines prospects to vasculopathy, elevated collagen synthesis, and progressive vascular fibrosis. In assessing SSc renal disease, the most important renal complication is usually SSc renal crisis (SRC), which is usually characterized by malignant hypertension, acute renal failure, and microangiopathy [3]. Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) refers to a group of autoimmune diseases characterized by necrotizing small vessel vasculitis, comprising granulomatosis with polyangiitis, microscopic polyangiitis, and eosinophilic granuloma with polyangiitis [4]. ANCA-associated glomerulonephritis (AGN), accounting for 6487.1% of AAV, is typified by kidney involvement, and a kidney biopsy is the current platinum standard for confirming its diagnosis [5,6]. Involvement of the vasculature in ANCA-positive vasculitis following SSc is rare [7]. Acute renal failure occurs in both SRC and AGN, especially in patients with an acute blood pressure increase. Unfortunately, accurately differentiating between SRC and AGN is usually hard, making it challenging for clinicians to correctly diagnose patients with these symptoms, and because the treatments for these conditions differ greatly PEPCK-C from each other, appropriate diagnosis is critical for achieving a good prognosis [8]. Here, we report the case of a 49-year-old male patient with SSc who developed biopsy-confirmed AAV and presented with acute renal insufficiency, and we review the literature on overlap between SSc and AAV. == Case presentation == The patient, a 49-year-old man, was admitted to our hospital for further evaluation of newly diagnosed acute renal insufficiency and highly elevated C-reactive protein (CRP) levels. He had a medical history of Raynauds phenomenon and was diagnosed with SSc 4 years previously. At that time, he reported no abnormality of renal function and urinary protein but was not followed up. He did not take any glucocorticoids or penicillamine during this time. In February 2020, 1 month before admission, he frequented a doctor in another hospital where he presented with generalized weakness, decreased appetite, oliguria, and bilateral lower extremity swelling. On physical examination, he was found to have elevated blood pressure (176/102 mmHg), elevated levels of blood urea nitrogen (23.17 mmol/L) and creatinine (1057 mol/L), proteinuria (+++), occult blood (+++), and a 24-h urine protein of 4.65 g. His CRP level was 112 mg/L, erythrocyte sedimentation rate (ESR) was 56 mm/h, and brain natriuretic peptide (BNP) level 17-AAG (KOS953) was 15,452 pg/mL. A kidney ultrasound showed no obvious abnormalities. A chest CT revealed bilateral pleural effusions and patchy shadows in both 17-AAG (KOS953) lung fields. The patient was treated with methylprednisolone (60 mg, daily), antibiotics, an antihypertensive drug, a diuretic treatment, and hemodialysis (three times per week), after which his creatinine level decreased to 366 mol/L, and his symptoms improved (Fig.1a). Eight days after these improvements, the methylprednisolone was discontinued.