Ankle Swelling: What Could Be Causing It

Why Ankles Swell: The Basic Physiology

Ankle swelling occurs when the balance between capillary hydrostatic pressure, plasma oncotic pressure, capillary permeability, and lymphatic drainage is disrupted. Gravity pulls fluid downward, so the ankles and feet are the first place excess interstitial fluid becomes visible.

Four mechanisms drive peripheral edema. Increased capillary hydrostatic pressure (from heart failure or venous obstruction) pushes fluid out of vessels. Decreased plasma oncotic pressure (from low albumin in nephrotic syndrome, cirrhosis, or malnutrition) reduces the force pulling fluid back in. Increased capillary permeability (from inflammation, infection, or allergic reactions) allows protein and fluid to leak into tissues. Impaired lymphatic drainage (from surgery, radiation, or filariasis) prevents normal fluid return 1.

The Starling equation describes this balance mathematically. In clinical practice, the question is simpler: which of these four mechanisms is broken? Bilateral swelling that worsens throughout the day and improves overnight typically reflects a systemic process. Unilateral swelling demands a different workup entirely 2.

Chronic Venous Insufficiency: The Most Common Culprit

Chronic venous insufficiency (CVI) is the leading cause of bilateral ankle edema in ambulatory adults, affecting an estimated 25% to 40% of women and 10% to 20% of men in Western populations 3.

Valves inside the deep and superficial leg veins normally prevent blood from pooling. When these valves fail (often after a prior DVT, pregnancy, obesity, or prolonged standing occupations), venous pressure in the lower legs rises. This elevated pressure forces fluid into surrounding tissues. Patients notice swelling that builds during the day and resolves partially overnight. Over months to years, the skin around the ankles develops characteristic changes: hemosiderin staining (brown discoloration), lipodermatosclerosis (hardened, woody skin), and eventually venous stasis ulcers near the medial malleolus.

The CEAP classification system grades CVI from C0 (no visible signs) through C6 (active ulceration). Duplex ultrasound confirms venous reflux lasting longer than 0.5 seconds in superficial veins or longer than 1.0 second in deep veins 4.

Treatment begins with graduated compression stockings (20 to 30 mmHg for mild disease, 30 to 40 mmHg for moderate to severe). The 2023 American Venous Forum guidelines recommend compression as first-line therapy and note that endovenous ablation or sclerotherapy may be appropriate for symptomatic patients with documented saphenous reflux 5.

Heart Failure: The Diagnosis You Cannot Miss

Heart failure causes bilateral ankle swelling through elevated central venous pressure and sodium/water retention mediated by the renin-angiotensin-aldosterone system. It is a diagnosis that requires prompt identification.

The prevalence of heart failure in the United States exceeds 6.7 million adults, according to 2022 AHA statistics 6. Peripheral edema is present in roughly 65% of patients with decompensated heart failure. The swelling is typically bilateral, pitting, and worse in the evening. Patients may also report orthopnea (needing extra pillows to breathe at night), paroxysmal nocturnal dyspnea, exertional breathlessness, and weight gain of 2 to 3 pounds over a few days.

B-type natriuretic peptide (BNP) measurement is the key initial test. A BNP below 100 pg/mL has a negative predictive value exceeding 90% for ruling out heart failure as the cause of edema 7. The Breathing Not Properly study (N=1,586) demonstrated that BNP at a cutoff of 100 pg/mL had 90% sensitivity and 76% specificity for diagnosing acute heart failure in the emergency department.

"BNP should be measured in all patients presenting with new unexplained bilateral edema, particularly those over age 50 or with cardiovascular risk factors," states the 2022 AHA/ACC/HFSA guideline for the management of heart failure 8.

Treatment targets the underlying cause: ACE inhibitors or ARNIs (sacubitril/valsartan), beta-blockers, mineralocorticoid receptor antagonists, SGLT2 inhibitors, and loop diuretics for volume management. The DAPA-HF trial (N=4,744) showed dapagliflozin reduced the composite of worsening heart failure or cardiovascular death by 26% (HR 0.74 to 95% CI 0.65 to 0.85) 9.

Deep Vein Thrombosis: When One Ankle Swells

Unilateral ankle swelling should always prompt consideration of deep vein thrombosis (DVT). This is a medical urgency.

DVT affects approximately 1 to 2 per 1,000 adults annually in the general population 10. Risk factors include recent surgery (especially orthopedic), immobilization, active cancer, oral contraceptive use, pregnancy, obesity, and prior DVT. The classic presentation is unilateral leg swelling with calf tenderness and warmth, though up to 50% of DVTs are clinically silent.

The Wells score stratifies pretest probability. Patients scoring 2 or higher are considered "DVT likely" and should undergo compression ultrasonography. Those with low probability (Wells score below 2) can have DVT excluded with a negative D-dimer (below 500 ng/mL) 11.

"The combination of a validated clinical prediction rule with D-dimer testing safely reduces the need for diagnostic imaging by 30% to 40%," notes the American College of Chest Physicians (ACCP) antithrombotic guideline, 10th edition 12.

When DVT is confirmed, anticoagulation with a direct oral anticoagulant (rivaroxaban 15 mg twice daily for 21 days, then 20 mg daily; or apixaban 10 mg twice daily for 7 days, then 5 mg twice daily) is preferred over warfarin for most patients per ACCP 2016 guidelines 12. Treatment duration ranges from 3 months for provoked DVT to indefinite for unprovoked or recurrent events.

Kidney Disease and Nephrotic Syndrome

The kidneys regulate sodium and water balance. When glomerular filtration drops or the glomerular barrier leaks protein, bilateral ankle edema follows.

Nephrotic syndrome (proteinuria exceeding 3.5 g per day, hypoalbuminemia, edema, and hyperlipidemia) causes edema through two pathways: reduced plasma oncotic pressure from albumin loss, and primary sodium retention by the collecting duct 13. Common causes in adults include membranous nephropathy, focal segmental glomerulosclerosis (FSGS), and diabetic nephropathy. A spot urine protein-to-creatinine ratio above 3.5 g/g confirms nephrotic-range proteinuria.

Chronic kidney disease (CKD) stages 4 and 5 (eGFR below 30 mL/min/1.73 m²) leads to edema through impaired sodium excretion even without heavy proteinuria. Approximately 37 million American adults have CKD, though most are in earlier stages 14.

Initial workup for suspected renal edema includes serum creatinine, BUN, albumin, urinalysis with microscopy, and a urine protein-to-creatinine ratio. Management depends on the underlying disease: loop diuretics for volume control, sodium restriction to below 2 g per day, ACE inhibitors or ARBs for proteinuria reduction, and disease-specific immunosuppression when indicated.

Liver Cirrhosis and Portal Hypertension

Cirrhosis produces ankle swelling through a combination of hypoalbuminemia (the liver synthesizes albumin), portal hypertension driving splanchnic vasodilation, and secondary hyperaldosteronism causing avid sodium retention.

Edema and ascites develop in roughly 50% of patients within 10 years of a cirrhosis diagnosis 15. The edema is bilateral, pitting, and often accompanied by abdominal distension, spider angiomata, palmar erythema, and jaundice. Serum albumin is typically below 3.0 g/dL.

The AASLD (American Association for the Study of Liver Diseases) practice guideline recommends sodium restriction (below 2 g/day) and spironolactone (starting at 100 mg daily, maximum 400 mg daily) as first-line diuretic therapy, with furosemide added if needed in a 100:40 mg ratio to maintain potassium balance 16.

Medication-Induced Ankle Swelling

Several drug classes cause peripheral edema as a direct pharmacologic effect. This is one of the most reversible causes.

Calcium channel blockers (CCBs) are the most frequent offenders. Amlodipine causes ankle edema in a dose-dependent fashion: approximately 5.6% at 5 mg daily versus 28.6% at 10 mg daily in registration trials 17. Nifedipine extended-release produces edema rates as high as 70% at maximum doses. The mechanism involves preferential arteriolar dilation without corresponding venodilation, raising capillary hydrostatic pressure in dependent tissues.

Other common culprits include:

• NSAIDs (ibuprofen, naproxen, celecoxib): promote renal sodium retention
• Thiazolidinediones (pioglitazone): increase renal sodium reabsorption via ENaC channels, with edema rates of 3% to 15% as monotherapy
• Gabapentin and pregabalin: peripheral edema in 2% to 8% of users
• Corticosteroids: mineralocorticoid effect causes sodium and water retention
• Estrogen-containing oral contraceptives and HRT: mild fluid retention in some users

The fix is usually straightforward. For CCB-induced edema, switching from amlodipine to an ACE inhibitor or ARB often resolves symptoms within 1 to 2 weeks. Adding an ACE inhibitor to amlodipine (rather than discontinuing) can also reduce edema by counteracting the postcapillary dilation mismatch 18.

Lymphedema: Non-Pitting and Progressive

Lymphedema produces non-pitting edema that does not resolve fully with elevation. This distinction from pitting edema is the key clinical clue.

Primary lymphedema (congenital or hereditary) accounts for a small fraction of cases. Secondary lymphedema is far more common and results from surgical lymph node dissection, radiation therapy (especially for pelvic, breast, or inguinal cancers), recurrent cellulitis with lymphatic scarring, or filariasis (the leading global cause, affecting over 120 million people in endemic regions) 19.

Early lymphedema may pit, but over time, fibrosis makes the tissue firm and non-pitting. The Stemmer sign (inability to pinch a fold of skin on the dorsum of the second toe) has high specificity for lymphedema. Lymphoscintigraphy confirms impaired lymphatic transport when the diagnosis is uncertain.

Management centers on complete decongestive therapy (CDT), which combines manual lymphatic drainage, multilayer compression bandaging, exercise, and skin care. Compression garments maintain volume reduction after the intensive phase.

Other Causes to Consider

Several less common but important conditions can present with ankle swelling.

Hypothyroidism produces myxedema, a non-pitting, boggy swelling caused by glycosaminoglycan deposition in the dermis. TSH screening identifies this quickly. Levothyroxine replacement resolves the edema over weeks to months.

Obstructive sleep apnea (OSA) can cause bilateral leg edema through pulmonary hypertension and right heart strain, even without overt left-sided heart failure. Polysomnography and echocardiography clarify the diagnosis.

Pregnancy commonly causes bilateral ankle edema, particularly in the third trimester, due to uterine compression of the inferior vena cava and increased blood volume. Sudden edema with hypertension and proteinuria raises concern for preeclampsia and requires urgent evaluation 20.

Idiopathic edema is a diagnosis of exclusion seen primarily in premenopausal women. It involves exaggerated postural sodium and water retention without identifiable cardiac, hepatic, renal, or venous disease.

Diagnostic Approach: How Clinicians Work Up Ankle Swelling

The evaluation begins with two questions: is the swelling unilateral or bilateral, and does it pit?

Unilateral pitting edema: DVT is the primary concern. Apply the Wells score. If DVT-likely, order compression ultrasound. If DVT-unlikely, check D-dimer. Also consider cellulitis (erythema, warmth, fever), Baker cyst rupture, or compartment syndrome after trauma.

Bilateral pitting edema: check BNP (heart failure), serum albumin (nephrotic syndrome, cirrhosis), creatinine and urinalysis (kidney disease), TSH (hypothyroidism), and review the medication list for CCBs, NSAIDs, and other offenders. Hepatic causes warrant liver function tests, INR, and abdominal ultrasound with Doppler.

Non-pitting edema: consider lymphedema (Stemmer sign, history of surgery/radiation) or myxedema (hypothyroidism). Lymphoscintigraphy may be needed.

A chest X-ray and echocardiogram are indicated when heart failure is suspected. Venous duplex ultrasound evaluates for DVT or chronic venous insufficiency. This structured approach, moving from clinical exam to targeted labs to imaging, avoids unnecessary testing while catching dangerous diagnoses 2.

When to Seek Emergency Care

Certain features accompanying ankle swelling demand same-day or emergency evaluation.

Acute unilateral leg swelling with calf pain and recent immobilization or surgery suggests DVT and possible pulmonary embolism. Bilateral edema with sudden dyspnea, orthopnea, or pink frothy sputum indicates decompensated heart failure or flash pulmonary edema. Ankle swelling with fever, rapidly spreading erythema, and systemic toxicity suggests necrotizing soft tissue infection. New bilateral edema with periorbital swelling, foamy urine, and blood pressure above 140/90 in a young adult may be acute glomerulonephritis.

Any patient with ankle swelling plus shortness of breath at rest, chest pain, or syncope needs emergency department evaluation. Weight gain exceeding 3 pounds in 48 hours in a patient with known heart failure warrants urgent diuretic adjustment per AHA guidelines 8.