Fibromuscular dysplasia

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

FMD changes the architecture of the arterial wall without the lipid plaque of atherosclerosis or the systemic inflammation of vasculitis. Multifocal medial fibroplasia commonly appears as beads in the middle and distal renal artery, whereas focal disease may resemble another stenosis. Because tissue is seldom obtained, diagnosis is radiological and clinical: morphology, distribution, age, risk profile and absence of an inflammatory syndrome all matter.

Presentation ranges from incidental imaging to renin-mediated hypertension, pulsatile tinnitus, dissection, aneurysm or infarction. Finding renal disease should not lead clinicians to ignore the neck and brain, while finding cervical FMD should trigger blood-pressure and renal assessment. The UK Kidney Association describes dedicated multidisciplinary input spanning renal medicine, neurology, interventional radiology and neuroradiology for complex cases.

Management targets the consequence rather than erasing every bead. Antihypertensive therapy controls most renal presentations; antiplatelet treatment is individualised to arterial and stroke risk because evidence for blanket primary prophylaxis is limited. Angioplasty can improve pressure in carefully selected renal disease, but cure is not guaranteed and restenosis or procedural dissection can occur, so expert selection and follow-up are central.

Key points

Fibromuscular dysplasia is an idiopathic, segmental, non-atherosclerotic and non-inflammatory disease of small and medium arteries that can cause stenosis, aneurysm, tortuosity and dissection.
Renal and cervical arteries are the commonest clinically involved beds, and more than one territory is often affected; symptoms depend on which artery and complication are present.
Think of renal FMD in a younger or middle-aged woman with early, abrupt or resistant hypertension, especially when imaging shows a mid-distal renal lesion rather than calcified ostial plaque.
Multifocal disease produces alternating stenoses and dilatations, the classic string-of-beads appearance; focal or tubular disease requires more careful exclusion of atherosclerosis, vasculitis and syndromic arteriopathy.
Headache and pulsatile tinnitus are common but non-specific. TIA, stroke, cervical-artery dissection, subarachnoid haemorrhage and visceral infarction are uncommon, time-critical manifestations.
CTA or MRA establishes the arterial pattern. Duplex can support renal surveillance but may miss distal, branch or cervicocephalic disease and is highly operator-dependent.
After FMD is confirmed in one bed, a specialist service should decide a one-time survey for other arterial territories and intracranial aneurysm, balancing diagnostic yield, renal function, radiation and contrast.
Blood-pressure treatment is first-line for renal FMD; ACE inhibition or an ARB is often useful but needs creatinine and potassium monitoring, particularly if both kidneys or a solitary kidney are supplied through disease.
Balloon angioplasty without a planned stent is the usual renal revascularisation technique for selected haemodynamically significant FMD with resistant hypertension; stenting is generally reserved for procedural bailout.
There is no routine curative genetic test and family screening is not automatic. Care includes smoking cessation, pregnancy counselling, symptom education and long-term arterial follow-up tailored to phenotype.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Idiopathic arterial-wall dysplasia

The underlying cause remains incompletely defined; segmental, non-inflammatory and non-atherosclerotic remodelling affects small and medium arteries, producing focal or multifocal lesions.

Possible familial susceptibility

A small familial signal is recognised, but no single diagnostic genotype exists and routine imaging of every relative is not established.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Segmental wall remodelling
The arterial wall develops focal stenosis or multifocal alternating narrowing and dilatation, with associated tortuosity, aneurysm and dissection.
2
Renal hypoperfusion
A clinically important renal-artery lesion can cause renin-mediated hypertension, which may begin young, accelerate unexpectedly or remain resistant to several medicines.
3
Dissection and aneurysm formation
Structurally vulnerable arterial segments may split or expand, compromising downstream flow or creating a rupture and embolic risk.
4
Multibed vascular injury
Involvement beyond renal arteries can affect cervicocephalic or visceral circulation, explaining pulsatile tinnitus, neurological events or organ infarction.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Renovascular presentation

Hypertension begins young, accelerates unexpectedly or remains high despite several agents, sometimes with an abdominal bruit, asymmetric renal size or a significant creatinine response to RAAS blockade.

Cervicocephalic presentation

Pulsatile tinnitus, persistent headache, cervical bruit or neck pain may accompany carotid or vertebral FMD, but each is non-specific and requires an appropriate neurological and vascular differential.

Arterial dissection signalRed flag

Sudden unilateral head or neck pain, partial Horner syndrome, retinal or cerebral ischaemia, acute coronary syndrome without usual plaque risk, or abrupt flank pain can indicate a dissected affected artery.

Aneurysmal complicationRed flag

Thunderclap headache, meningism, collapse or acute abdominal pain raises concern for intracranial or visceral aneurysm rupture. An unruptured aneurysm may instead be discovered during multisite imaging.

Typical imaging morphology

Alternating narrowings and dilatations create a string-of-beads pattern in a mid-distal artery. A single focal stenosis can be FMD but demands stronger clinicoradiological discrimination from plaque and vasculitis.

Multivessel phenotype

Renal disease coexists with carotid, vertebral, mesenteric, iliac or coronary involvement, arterial tortuosity, aneurysm or prior spontaneous dissection. Symptoms and surveillance then cannot be organised by one specialty alone.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Validated blood pressure, creatinine, potassium and urine ACRFirst step
Why
Quantify the renal consequence, establish treatment safety and identify a competing intrinsic nephropathy.
Interpretation and limitations
Use home or ambulatory readings where needed. Renal FMD can cause severe hypertension with relatively preserved urine findings; substantial haematuria or proteinuria needs another explanation as well.
02
Renal CT angiography
Why
Demonstrate focal or multifocal stenosis, aneurysm, dissection, renal infarction and accessory-artery anatomy.
Interpretation and limitations
Mid-distal beading without calcified plaque supports multifocal FMD. Review source images with vascular radiology because small branch lesions and motion can alter interpretation.
03
MR angiography
Why
Map renal or cervicocephalic arteries when avoiding ionising radiation or iodinated contrast is particularly valuable.
Interpretation and limitations
Resolution, artefact, device compatibility and gadolinium suitability vary. A normal study of limited quality should not overrule a compelling acute dissection syndrome.
04
Targeted duplex ultrasonography
Why
Provide a radiation-free haemodynamic assessment and follow a known accessible renal or cervical lesion.
Interpretation and limitations
Expertise and local criteria matter. Renal FMD commonly sits beyond the ostium, so bowel gas, tortuosity and distal location can produce a false-negative or misleading velocity.
05
Specialist multisite arterial assessment
Why
Look once for additional FMD, dissection and intracranial or visceral aneurysm after disease is confirmed in one bed.
Interpretation and limitations
CTA or MRA coverage and later surveillance are individualised by an FMD MDT; repeat whole-body radiation at fixed intervals is not an evidence-based default.
06
Catheter angiography and pressure assessment
Why
Resolve anatomy and physiological significance when renal angioplasty is already being considered.
Interpretation and limitations
Digital subtraction angiography has high resolution but creates arterial, contrast and radiation risk. It should be coupled to a treatment plan, with stenting available for bailout rather than routine deployment.
07
Inflammatory and genetic testing when phenotype is atypical
Why
Exclude vasculitis, connective-tissue disease or a defined inherited arteriopathy when clinical features point away from isolated FMD.
Interpretation and limitations
Normal inflammatory markers support but do not prove FMD. Broad genetic panels are not routine because no single diagnostic FMD genotype exists; genetics input should follow syndromic clues or a striking pedigree.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Atherosclerotic renal artery stenosis

Older age, calcified ostial plaque and widespread atherosclerosis favour atherosclerotic disease, whereas mid-distal beading in a younger patient supports FMD.

Large-vessel vasculitis

Systemic inflammation, vessel-wall thickening and long smooth stenoses suggest arteritis rather than the non-inflammatory beaded or focal FMD pattern.

Inherited connective-tissue arteriopathy

Marked joint, skin, craniofacial or family aneurysm features should prompt assessment for syndromic vascular disease rather than assuming isolated FMD.

Primary hypertension

Common essential hypertension lacks a convincing arterial lesion and renal perfusion phenotype; incidental tortuosity should not be presumed causal without specialist correlation.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01New diagnosisConfirm pattern and map consequencesFirst stepCTA, MRA or angiography reports renal or cervical beading or a compatible focal lesion.

1Ask radiology to confirm morphology and exclude ostial plaque, inflammatory wall thickening and artefact; record every involved bed, aneurysm, dissection and infarct.
2Assess blood pressure, kidney function, urine ACR and neurological history, then refer to a renal-vascular or FMD service for coordinated review.
3Agree one-time multisite and intracranial-aneurysm assessment, prevention, pregnancy advice and a symptom-led surveillance schedule with the patient.

02Renal hypertensionTreat pressure before procedureRenal FMD is associated with confirmed sustained hypertension but no acute organ injury.

1Start or optimise guideline-based antihypertensive therapy, often including monitored ACE inhibition or an ARB, and address smoking, salt intake and adherence.
2Use out-of-office readings and serial renal biochemistry to determine whether pressure is controlled and whether the lesion is clinically consequential.
3For persistent hypertension despite at least three appropriate agents and severe haemodynamically relevant disease, discuss balloon angioplasty in an experienced MDT rather than requesting primary stenting.

03Neurological eventUse the standard emergency pathwayFocal deficit, amaurosis, sudden severe headache, painful Horner syndrome or acute neck pain occurs in known or suspected FMD.

1Activate the local stroke or subarachnoid-haemorrhage pathway immediately and obtain time-critical brain and arterial imaging; do not let the FMD label delay reperfusion assessment.
2Define infarction, haemorrhage, cervical dissection and aneurysm before choosing antiplatelet, anticoagulant or endovascular treatment because their risks differ sharply.
3After stabilisation, coordinate stroke, neuroradiology and FMD follow-up and update the multisite arterial record and safety-netting advice.

04Incidental diseaseAvoid overtreatment while preserving surveillanceCharacteristic FMD is discovered in an asymptomatic person with controlled pressure and no threatened organ.

1Confirm the image and establish baseline BP, kidney function and neurological symptoms rather than attributing every headache to the arterial finding.
2Discuss smoking cessation, exercise and trauma questions, pregnancy planning and whether an individual antiplatelet indication exists after bleeding review.
3Set follow-up by lesion, aneurysm and dissection history; reserve repeat cross-sectional imaging for a specialist-defined question or new clinical change.

Key medicines and prescribing safety4 treatments · regimens, roles and cautions

Counters renin-driven hypertension in renal FMD and is often an effective foundation for medical control.

ACE inhibitor or angiotensin-receptor blocker

Select a licensed agent and titrate gradually under NICE hypertension guidance and the local renal formulary.

Measure creatinine and potassium before and after initiation or titration; bilateral renal involvement, solitary-kidney disease, dehydration, pregnancy, hyperkalaemia and NSAIDs materially change safety.

Achieves pressure targets when RAAS blockade alone is insufficient or cannot safely be used.

Additional antihypertensive therapy

Use licensed calcium-channel blocker, thiazide-like diuretic or other agents in stepped combinations tailored to physiology.

Verify sustained resistance and adherence before adding drugs; review postural symptoms, oedema, electrolytes, kidney function, pregnancy potential and interaction with acute stroke or dissection management.

May reduce thromboembolic risk in selected cerebrovascular FMD, prior dissection or another established antiplatelet indication.

Aspirin when individually indicated

Aspirin 75 mg once daily may be chosen after specialist assessment of arterial and bleeding risk.

Evidence does not justify automatic lifelong primary prophylaxis for every incidental bead; consider gastrointestinal or intracranial bleeding, aneurysm status, pregnancy and concurrent anticoagulation.

Can improve otherwise resistant renin-mediated hypertension when a severe renal FMD lesion is haemodynamically important.

Percutaneous transluminal renal angioplasty

Balloon treatment is performed by an expert interventional service, with stenting reserved chiefly for procedural bailout.

Hypertension may improve without being cured; arterial dissection, perforation, renal infarction, access bleeding and restenosis require consent and structured follow-up.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Resistant renovascular hypertension

Persistent renin activation can make blood pressure difficult to control and increase stroke, cardiac and chronic kidney risk.

Renal ischaemia or infarction

Severe stenosis, branch disease or dissection may reduce viable renal mass, producing flank pain, acute dysfunction or chronic ischaemic nephropathy.

Cervical-artery dissection and stroke

Dissection can generate local pain, thromboembolism or reduced cerebral flow, leading to transient ischaemia or completed stroke.

Intracranial aneurysm rupture

Associated aneurysmal disease can cause subarachnoid haemorrhage, which explains selective specialist screening and urgent assessment of sudden severe neurological symptoms.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Track home blood pressure, medicine burden and postural tolerance; improvement after angioplasty is not synonymous with safe withdrawal of all treatment.
Repeat creatinine and potassium after RAAS-blocker changes and during dehydrating illness, and re-evaluate promptly if filtration deteriorates or urine output falls.
At specialist review, ask specifically about pulsatile tinnitus, new headache phenotype, transient neurology, neck or flank pain and symptoms of coronary or mesenteric ischaemia.
Follow known aneurysms, dissections and treated arterial segments with the modality and interval chosen by the relevant vascular or neuroradiology MDT; minimise unnecessary cumulative radiation.
After renal angioplasty, document procedural result, kidney function, BP response and duplex or cross-sectional surveillance for recurrent stenosis.
Review pregnancy intentions before RAAS blockade and before contrast imaging; established FMD warrants joint obstetric and vascular planning rather than reflex advice against pregnancy.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Location separates mechanisms

Atherosclerotic renal disease favours the ostium and proximal artery, whereas multifocal FMD usually affects the middle or distal segment and may extend into branches.

Beads are a phenotype

The string-of-beads sign supports multifocal FMD, but treatment depends on pressure, organ ischaemia, aneurysm and dissection rather than visual drama.

Headache needs discrimination

Many people with FMD have ordinary headache; a thunderclap onset, new focal deficit or painful Horner syndrome is qualitatively different and demands emergency imaging.

Multisystem does not mean inflammatory

Several affected arterial beds can occur without raised inflammatory markers because FMD is a structural arteriopathy, not a medium-vessel vasculitis.

Angioplasty is usually stent-sparing

Unlike calcified ostial plaque, renal FMD often responds to balloon dilatation alone; a permanent stent is mainly a rescue for complication or inadequate result.

Relatives need judgement

A small familial signal exists, but routine imaging of every relative is not established; symptoms, syndromic features and specialist genetic advice guide testing.

11Common pitfallsFrequent interpretation and management errors.

01
Calling an ostial calcified plaque in an older vascular patient fibromuscular dysplasia because the report uses the word stenosis.
02
Treating pulsatile tinnitus or chronic headache as proof of cervical FMD without appropriate imaging and alternative assessment.
03
Missing renal and intracranial assessment after FMD is confirmed in another arterial bed.
04
Offering aspirin automatically without reviewing aneurysm, haemorrhage, pregnancy, gastrointestinal risk and concurrent antithrombotics.
05
Placing a routine renal stent where balloon angioplasty alone is the specialist preferred technique.
06
Repeating whole-body CTA annually without an MDT-defined question, accumulating radiation and incidental findings.