A 48-year-old woman comes to the emergency department due to worsening headache, blurred vision, and nausea for the past several days. She also has had decreased urine output. Medical history is significant for systemic sclerosis. Blood pressure is 190/110 mm Hg and pulse is 96/min. Physical examination shows diffuse skin thickening involving the hands, face, and anterior chest. There are no focal neurologic deficits, but a flame-shaped retinal hemorrhage is present. Laboratory studies reveal elevated serum blood urea nitrogen and creatinine levels, which were within normal limits during a recent office visit. Urine microscopy shows no sediment. A primary injury to which of the following structures is the most likely cause of this patient's acute kidney injury?
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Systemic sclerosis (SS) (ie, scleroderma) is an autoimmune disease that damages connective tissue and small blood vessels throughout the body. This patient's acute renal failure and severe hypertension (eg, retinal hemorrhage, headache) are consistent with a life-threatening complication of SS known as scleroderma renal crisis (SRC). SRC is caused by immune-mediated injury to small renal vessels that typically spares the glomerular capillaries; therefore, dysmorphic red blood cells (RBCs) and RBC casts are not present on urine microscopy, unlike in patients with glomerulonephritis (Choice C). Vascular changes in SRC include:
Histopathologic changes in SRC are similar to malignant nephrosclerosis caused by severe primary hypertension. Patients with severe primary hypertension develop these changes as a direct result of vascular barotrauma. In contrast, patients with SRC develop hypertension due to vascular narrowing and obliteration, which results in renal hypoperfusion. Renal hypoperfusion leads to renal failure and activation of the renin-angiotensin-aldosterone system (RAAS), which promotes systemic vasoconstriction, thereby resulting in severe hypertension. Therefore, first-line treatment for SRC is RAAS blockade with an ACE inhibitor, even in the presence of renal failure.
(Choice A) Vasculitis of large systemic vessels is a characteristic finding in Takayasu arteritis, which can lead to renovascular hypertension via inflammation-induced narrowing of the large renal artery. However, acute renal failure has only rarely been described in patients with Takayasu arteritis, likely because bilateral renal artery involvement would be necessary in most patients.
(Choice B) Obstruction of the postrenal urinary tract (eg, bilateral ureteral compression, bladder outlet obstruction) can lead to renal failure, but this patient's skin changes and severe hypertension make SRC more likely.
(Choices D and E) Tubulointerstitial diseases (eg, interstitial nephritis) typically cause an active urine sediment (eg, white blood cell casts). Tubulointerstitial involvement is sometimes seen with certain autoimmune diseases (eg, sarcoidosis, Sjögren syndrome), but it is not typical of SS.
Educational objective:
Scleroderma renal crisis (SRC) is a life-threatening complication of systemic sclerosis characterized by acute renal failure and severe hypertension. SRC is caused by immune-mediated injury to small renal vessels that leads to reduced renal perfusion due to vascular narrowing and obliteration.