What is the diagnosis and treatment for a 17-year-old male with bilateral pedal edema, erythematous patches resembling cellulitis, and episodes of hematuria, presenting with a 3-day history of pedal edema?

Diagnosis: Post-Infectious Glomerulonephritis (Most Likely Acute Post-Streptococcal Glomerulonephritis)

This 17-year-old male most likely has acute post-infectious glomerulonephritis presenting with the classic triad of hematuria (red urine), edema (bilateral pedal edema), and skin findings that may represent either concurrent cellulitis or erythema from the underlying glomerular disease.

Clinical Reasoning

The combination of bilateral pedal edema, episodes of hematuria (red urine), and erythematous patches in a young male strongly suggests acute glomerulonephritis rather than primary cellulitis:

• True cellulitis is typically unilateral and presents with poorly demarcated erythema, warmth, and tenderness 1, 2
• Bilateral pedal edema with hematuria points to a systemic glomerular process causing proteinuria, hypoalbuminemia, and fluid retention 3
• The red patches may represent either concurrent skin infection (which can trigger post-streptococcal glomerulonephritis) or inflammatory changes from the underlying renal disease 1

Immediate Diagnostic Workup Required

Essential laboratory investigations to confirm diagnosis:

• Urinalysis with microscopy to assess for red blood cell casts (pathognomonic for glomerulonephritis), proteinuria, and hematuria 3
• Serum creatinine and blood urea nitrogen to evaluate renal function 3
• Serum albumin (expect <3.5 g/dL if nephrotic-range proteinuria) 3
• 24-hour urine protein or spot urine protein-to-creatinine ratio to quantify proteinuria 4
• Complement levels (C3, C4) - low C3 with normal C4 suggests post-streptococcal glomerulonephritis
• Anti-streptolysin O (ASO) titer and anti-DNase B to confirm recent streptococcal infection
• Complete blood count to assess for anemia or infection 3

Additional considerations:

• Blood cultures if febrile to rule out systemic infection 1
• Throat or skin culture if active infection suspected 1
• Renal ultrasound to assess kidney size and rule out structural abnormalities 3

Treatment Approach

For the Glomerulonephritis Component:

Supportive management is the cornerstone:

• Furosemide for edema control with daily monitoring of fluid intake/output, targeting 0.5-1 kg weight loss per day 3, 5
• Strict sodium and fluid restriction to manage volume overload 3
• ACE inhibitor (enalapril) to reduce proteinuria and provide renoprotection 3
• Monitor electrolytes closely during diuretic therapy, particularly sodium and potassium 5
• Blood pressure control targeting <125/80 mmHg if proteinuria is significant 4

Discontinue diuretics if severe hyponatremia, progressive renal failure, or incapacitating muscle cramps develop 5

For Potential Concurrent Cellulitis:

If the erythematous patches represent true cellulitis (unilateral distribution, warmth, tenderness):

• First-line oral antibiotic: Cephalexin or penicillin VK targeting streptococci, as MRSA is uncommon in typical cellulitis 4, 1
• Duration: 5 days for uncomplicated cellulitis is as effective as 10 days 4
• Elevation of affected extremities to promote gravity drainage of edema 4
• Treat predisposing factors such as tinea pedis or skin trauma 4

MRSA coverage is NOT routinely needed unless:

• Penetrating trauma or injection drug use
• Purulent drainage present
• Previous MRSA infection documented 4

If Cellulitis Confirmed with Slow Response:

Consider adding systemic corticosteroids (prednisone 40 mg daily for 7 days) in non-diabetic patients to reduce inflammation and hasten resolution, though this must be weighed against potential worsening of fluid retention from the glomerulonephritis 4

Critical Pitfalls to Avoid

Do not assume bilateral pedal edema is from cellulitis alone - bilateral presentation strongly suggests systemic disease (cardiac, renal, hepatic, or medication-induced) rather than infection 6, 1

Do not delay nephrology consultation if laboratory findings confirm glomerulonephritis, as some forms may require immunosuppressive therapy 4

Monitor for complications:

• Hypertensive emergency (can occur with acute glomerulonephritis)
• Acute kidney injury requiring dialysis
• Pulmonary edema from volume overload 3

If furosemide fails to control edema, consider adding thiazide diuretic for sequential nephron blockade or spironolactone for resistant edema 5

Prognosis and Follow-up

Post-streptococcal glomerulonephritis in adolescents typically has excellent prognosis with supportive care, with most patients recovering full renal function within weeks to months. However, close monitoring of renal function, proteinuria, and blood pressure is essential to identify the minority who develop chronic kidney disease 4.