Abstract
Summary
Fibromuscular dysplasia can cause renovascular hypertension. Since fibromuscular dysplasia may be underdiagnosed, precise diagnosis and management are crucial, especially for young women. A 20-year-old woman with hypertension and hypokalemia was referred to our hospital for further evaluation of secondary hypertension. At the previous hospital, her blood pressure was 160/110 mmHg and the serum potassium level was 2.9 mEq/L. The equilibrium phase on contrast-enhanced computed tomography revealed a low-density area in the upper median portion of the right kidney. On admission to our hospital, her blood pressure was 141/96 mmHg under 5 mg of amlodipine. Laboratory tests revealed plasma renin activity of 11.3 ng/mL/h and plasma aldosterone concentration of 117.1 pg/mL. Renal venous sampling of active renin concentration showed a right-to-left renin ratio of 3.13, confirming a significant increase in renin secretion from the right kidney. Selective reno-angiography detected focal stenosis with adjacent aneurysmal dilation and tortuosity in the proximal branch of the right renal artery. She was diagnosed with branch artery fibromuscular dysplasia and successfully treated with percutaneous transluminal angioplasty. After the treatment, she was free from hypertension and hypokalemia without any medications. Since branch artery fibromuscular dysplasia is sometimes difficult to diagnose, contrast-enhanced computed tomography can be a promising diagnostic tool as shown in this case. Concerning treatment, our patient was treated with percutaneous transluminal angioplasty, which should be considered for women of reproductive age because recommended antihypertensive medications can be teratogenic even in the first trimester of pregnancy.
Learning points
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Although branch artery fibromuscular dysplasia (FMD) is sometimes difficult to diagnose, it should be considered in patients with high-renin, high-aldosterone hypertension.
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Branch artery FMD can present with a low-density area of the kidney on contrast-enhanced computed tomography, as shown in this case.
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Percutaneous transluminal angioplasty (PTA) can be an appropriate treatment for branch artery FMD, especially in young female patients.
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PTA may immediately improve hypertension and hypokalemia without the need for medications.
Background
Fibromuscular dysplasia (FMD) is a non-atherosclerotic non-inflammatory disease with an unidentified cause although some risk factors including genetic predispositions have been proposed (1, 2). FMD affects renal arteries in most cases (65–70%) and accounts for less than 10% of renovascular hypertension (RVH) (2, 3). FMD might be underdiagnosed although its prevalence in the general population is still uncertain (4). As FMD is frequently observed in young women, the appropriate diagnosis and management are essential, especially for patients of childbearing age (1, 2, 3).
In this report, we present a case of a young woman who was diagnosed with branch artery FMD and underwent successful ballooning therapy. This case suggests that contrast-enhanced computed tomography (CECT) may serve as a possible diagnostic tool for branch artery FMD.
Case presentation
A 20-year-old woman with hypertension and hypokalemia was referred to our hospital. At the previous hospital, her blood pressure was 160/110 mmHg with hematuria and proteinuria. The serum potassium level was 2.9 mEq/L, and 2400 mg (32 mEq) potassium chloride was administered. The tests for the renin–angiotensin–aldosterone system revealed a plasma renin activity (PRA) of 28.9 ng/mL/h (normal range: 0.2–2.7 ng/mL/h), and her plasma aldosterone concentration (PAC) was 101 pg/mL, as evidenced by the chemiluminescent enzyme immunoassay (normal range: 4–82 pg/mL). The equilibrium phase on CECT revealed a low-density area in the upper medial portion of the right kidney with no artery stenosis (Fig. 1). The arterial phase on CECT showed no low-density area in the kidneys (Fig. 2). The patient was referred to our hospital for further evaluation of secondary hypertension. Her blood pressure at admission was 141/96 mmHg under 5 mg of amlodipine. On physical examination, all systems were found to be within normal range.
(A) The transverse plane and (B) the coronal plane in the equilibrium phase on CECT. Both planes show a low-density area in the upper medial portion of the right kidney (red arrows).
Citation: Endocrinology, Diabetes & Metabolism Case Reports 2023, 4; 10.1530/EDM-23-0054
The transverse plane in the arterial phase on CECT. No low-density areas are detected in the arterial phase.
Citation: Endocrinology, Diabetes & Metabolism Case Reports 2023, 4; 10.1530/EDM-23-0054
She had no medical history other than frequent headaches for 3 years. She had no family history of hypertension and did not smoke cigarettes or consume alcohol or drugs.
The differential diagnosis of high-renin, high-aldosterone hypertension comprises RVH, including atherosclerotic renal artery stenosis, focal or multifocal FMD, Takayasu’s arteritis, and renal arteriovenous fistula, as well as renin-producing tumor (3, 5). Since our patient was a young woman without a history of smoking and CECT showed a segmental low-density area in the right kidney, the probable diagnosis was most likely to be non-atherosclerotic RVH, especially with a focal renal aortic lesion.
Investigation
Laboratory tests revealed a serum potassium level of 4.1 mEq/L under 2400 mg (32 mEq) of potassium chloride, a C-reactive protein level of less than 0.01 mg/L, and a creatinine level of 0.65 mg/dL. PRA was 11.3 ng/mL/h, PAC was 117.1 pg/mL, and other hormones including serum cortisol and catecholamine were all within normal range. Urinalysis showed no hematuria or proteinuria.
Abdominal duplex ultrasonography was performed twice, and no artery stenosis was detected. A renin provocation test with 50 mg of captopril showed a significant increase in PRA (9.1 ng/mL/h at baseline, and 43.7 ng/mL/h 90 min later). Angiography showed that the right kidney was supplied by two arteries (ventral and dorsal renal arteries), and the left kidney was supplied by a single artery (Fig. 3). The selective reno-angiography of the right dorsal renal artery revealed focal stenosis with adjacent aneurysmal dilation and tortuosity in the proximal branch, confirming branch artery FMD (Fig. 4) (3). The renal venous sampling revealed that active renin concentration (ARC) was 105.7 pg/mL and 33.8 pg/mL in the right and left renal veins, respectively. The right-to-left renin ratio was 3.13 (>1.5), which confirmed a significant increase in renin secretion from the right kidney. Angiographic and endocrinological findings firmly demonstrated that hypertension was caused by renin secretion from the hypoperfusion area distal to the stenotic branch of the right dorsal renal artery.
The aortography. The right kidney is supplied with the following two arteries: a ventral renal artery and a dorsal renal artery. The left kidney is supplied with a single artery.
Citation: Endocrinology, Diabetes & Metabolism Case Reports 2023, 4; 10.1530/EDM-23-0054
The selective reno-angiography of the right dorsal renal artery. The stenosis with adjacent aneurysmal dilation and tortuosity was detected at the branch of the right dorsal renal artery (red arrow).
Citation: Endocrinology, Diabetes & Metabolism Case Reports 2023, 4; 10.1530/EDM-23-0054
Treatment
Although hypertension was largely well managed at our hospital, the patient wished to undergo treatment for the lesion and discontinue all the medications for possible pregnancy in the future. She was referred to the radiology department for percutaneous transluminal angioplasty (PTA) of the stenotic lesion. During the procedure, the lesion was successfully treated with a 3.0 mm × 20 mm balloon (Coyote MR, Boston Scientific, MA, USA), and after PTA, it was confirmed to be dilated (Fig. 5A and B, respectively). After the procedure, several stenotic lesions appeared in the trunk of the artery, which we suppose were transient spasms due to the mechanical stimuli of the catheters (Fig. 5B). To determine the treatment’s effect, CECT was performed immediately after PTA. The equilibrium phase on CECT showed that the low-density area was less clear than in the image before the procedure, and the arterial phase on CECT revealed no low-density areas, as before (Fig. 6A and B, respectively).
(A) PTA for the stenotic lesion and (B) the successful dilation in selective reno-angiography. (A) The lesion was dilated with a balloon catheter. (B) After PTA, the lesion was successfully dilated (red arrow). There were some stenoses in the trunk of the artery (blue arrows), which were suspected to be transient spasms caused by mechanical stimuli of catheters and were expected to resolve gradually.
Citation: Endocrinology, Diabetes & Metabolism Case Reports 2023, 4; 10.1530/EDM-23-0054
The transverse planes in (A) the equilibrium phase and (B) the arterial phase on CECT. (A) The low-density area was still visible, although it was less clear compared with that on CECT prior to PTA. (B) No low-density areas were detected in the arterial phase.
Citation: Endocrinology, Diabetes & Metabolism Case Reports 2023, 4; 10.1530/EDM-23-0054
Outcome and follow-up
The next day, the blood pressure was normalized (122/62 mmHg) without any antihypertensive medications, and both ARC and PAC significantly decreased (4.2 pg/mL and 9.2 pg/mL, respectively). The patient was discharged 6 days after PTA without any adverse events. Although she had frequent headaches over the past 3 years, contrast-enhanced magnetic resonance angiography of the head and neck revealed no stenosis.
Three months after the discharge, the patient was stable and free from hypertension and hypokalemia and required no medications.
Discussion
We report the case of a young woman with hypertension and hypokalemia, who was finally diagnosed with RVH due to branch artery FMD both angiographically and endocrinologically. To the best of our knowledge, this is the first case report of a segmental low-density area of the kidney on CECT as a possible clue for diagnosing branch artery FMD.
Retrospectively, the segmental low-density area on CECT was probably caused by the stenotic branch artery. First, we could not identify the CECT findings as key images of branch artery stenosis due to FMD. However, since selective reno-angiography revealed a stenotic lesion, the low-density area was presumably caused by the renal hypoperfusion distal to the stenosis. The arterial phase on CECT was unremarkable possibly because the narrow window width made it impossible to detect differences between the hypoperfusion and other areas. After PTA, the low-density area was blurred in the equilibrium phase, although it still remained. As the CECT was performed immediately after PTA, the area might not be fully perfused. It was possible that several months after the procedure, the low-density area might have disappeared. However, we did not perform CECT again because of her good clinical course and the preference for less radiation for young female patients.
CECT can be a promising tool to diagnose branch artery FMD, which is sometimes so difficult to diagnose that even angiography, as well as CTA, failed to confirm it (6). In three case reports of FMD presenting with segmental hypoperfusion areas, selective reno-angiography or angiography detected segmental hypoperfusion areas (7, 8, 9). In one case report, a segmental low-density area on CECT was also detected simultaneously with CT angiography (8). In this case, we had CECT images beforehand, duplex ultrasound failed to detect artery stenosis twice, and angiography finally confirmed branch artery FMD. Therefore, CECT might be useful in helping detect branch artery FMD.
Since the patient was a young female, she was treated with PTA rather than medication. Although the recommended medications for FMD are angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers, they can be teratogenic even in the first trimester of pregnancy and should be discouraged in women of reproductive age (3, 10). In contrast, PTA is effective for branch artery FMD without risk of teratogenicity (8). Therefore, PTA was appropriate in this case, and indeed, the patient was successfully treated with PTA, after which hypertensive medications were discontinued.
In conclusion, it is important to consider branch artery FMD in patients with hypertension who present with a segmental low-density renal area on CECT.
Declaration of interest
The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the case study reported.
Funding
This research did not receive any specific grant from any funding agency in the public, commercial, or not-for-profit sector.
Patient consent
Written informed consent for publication of her clinical details and clinical images was obtained from the patient.
Author contribution statement
YK wrote the first draft of the manuscript, and all the other authors critically reviewed it. All authors were involved in the assessment and treatment of the patient. All authors reviewed and approved the final draft of the manuscript.
Acknowledgement
We would like to thank Editage (www.editage.com) for English language editing.
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