How should I manage an adult patient with metastatic melanoma and a necrotic wound who now has calcium‑oxalate crystals in the urine?

Management of Calcium Oxalate Crystalluria in Metastatic Melanoma with Necrotic Wound

Immediate Priority: Rule Out Ethylene Glycol Toxicity

The presence of calcium oxalate crystals in urine in a patient with metastatic melanoma and necrotic wound requires immediate exclusion of ethylene glycol (antifreeze) poisoning, which presents with calcium oxalate and hippurate crystals in urine along with high anion gap metabolic acidosis. 1

• Obtain arterial blood gas, serum electrolytes, anion gap, osmolar gap, serum ethylene glycol level, and lactate immediately 1
• Check for metabolic acidosis with elevated anion gap (>12 mEq/L), which would suggest toxic ingestion rather than simple crystalluria 1
• Ethylene glycol toxicity is a medical emergency requiring fomepizole or ethanol therapy plus hemodialysis 1
• The clinical context of metastatic melanoma with necrotic wound raises concern for altered mental status or pain medication use that could mask intentional or accidental ingestion 1

If Toxicology is Negative: Address Crystalluria Management

Aggressive Hydration Protocol

Target 3.5-4 liters of oral fluid intake daily in adults to achieve urine output of at least 2.5 liters per day, as this is the cornerstone intervention to prevent calcium oxalate supersaturation and stone formation. 2, 3

• Distribute fluid intake throughout day and night to maintain consistent urine dilution 4
• Monitor urine output to ensure adequate diuresis above 1 ml/kg/h 2
• In patients with metastatic disease and potential renal involvement, adjust fluid goals based on renal function 2

Dietary Modifications

Maintain normal dietary calcium intake of 1,000-1,200 mg per day from food sources—do not restrict calcium, as this paradoxically increases oxalate absorption and stone risk. 2, 3, 4

• Limit sodium intake to 2,300 mg daily to reduce urinary calcium excretion 2, 3
• Reduce non-dairy animal protein to 5-7 servings per week 2, 4
• Avoid extremely high-oxalate foods (spinach, rhubarb, chocolate, nuts, beetroot, tea, wheat bran) but do not impose strict low-oxalate diet unless confirmed hyperoxaluria 2, 3
• Consume calcium with meals to enhance gastrointestinal binding of oxalate 2
• Avoid vitamin C supplements exceeding 1,000 mg/day, as vitamin C is metabolized to oxalate 2, 3

Metabolic Evaluation

Obtain 24-hour urine collection within 6 months to measure volume, pH, calcium, oxalate, uric acid, citrate, sodium, potassium, and creatinine to identify metabolic abnormalities and guide pharmacologic therapy. 2, 3, 4

• At least two positive urine assessments showing elevated oxalate are recommended to confirm hyperoxaluria 3
• Urinary oxalate >1 mmol/1.73 m² per day is strongly suggestive of primary hyperoxaluria and requires exclusion of enteric causes 3
• In cancer patients, consider secondary causes including chemotherapy effects, tumor lysis, or paraneoplastic syndromes 2

Pharmacologic Management Based on Metabolic Profile

If 24-hour urine shows hypocitraturia (citrate <400 mg/day), initiate potassium citrate 30-80 mEq/day in 3-4 divided doses to achieve urinary pH of 6.2-6.5 and citrate levels of 400-700 mg/day. 2, 4, 5

• Potassium citrate reduces stone formation rate by 80-98% in hypocitraturic calcium oxalate nephrolithiasis 5
• Use potassium citrate rather than sodium citrate, as sodium load increases urinary calcium excretion 2, 4
• For hypercalciuria (>250 mg/day in women, >300 mg/day in men), add thiazide diuretics (hydrochlorothiazide 50 mg daily or chlorthalidone 25-50 mg daily) 2, 4
• For hyperuricosuria (>800 mg/day) with normal urinary calcium, consider allopurinol 2, 4

Special Considerations for Metastatic Melanoma Context

Wound-Related Factors

Necrotic wounds in metastatic melanoma can contribute to systemic inflammation and altered renal handling of calcium and oxalate through cytokine-mediated effects on tubular function. 1

• Aggressive wound debridement and management may improve overall metabolic status 1
• Consider palliative radiation therapy for necrotic melanoma lesions causing significant tissue breakdown 1
• Monitor for tumor lysis syndrome if patient is receiving systemic therapy, which can precipitate crystalluria 1

Prognosis and Treatment Goals

In patients with disseminated metastatic melanoma, treatment decisions should balance stone prevention against quality of life and overall prognosis. 1

• For patients with limited life expectancy (<6 months), focus on hydration and symptom management rather than aggressive metabolic workup 1
• For patients with better prognosis or on effective systemic therapy (immunotherapy, targeted therapy), pursue full metabolic evaluation and pharmacologic management 1
• Avoid unnecessary procedures or interventions that do not improve quality of life in advanced disease 1

Common Pitfalls to Avoid

• Never restrict dietary calcium—this is the most common error and paradoxically increases stone risk by increasing urinary oxalate 2, 3, 4
• Do not overlook ethylene glycol toxicity in the differential diagnosis, especially in patients with altered mental status or access to antifreeze 1
• Do not rely on spot urinalysis crystalluria alone to diagnose primary hyperoxaluria—always confirm with quantitative 24-hour urine oxalate measurement 3
• Avoid using calcium supplements rather than dietary calcium sources, as supplements taken between meals do not bind intestinal oxalate 2
• Do not use sodium citrate instead of potassium citrate, as the sodium load can increase urinary calcium 2, 4

Nephrology Referral Indications

Refer to nephrology immediately if there is evidence of renal dysfunction (creatinine >1.5 mg/dL or eGFR <60 ml/min/1.73 m²), progressive decline in kidney function, heavy crystalluria (>200 whewellite crystals per cubic millimeter suggesting primary hyperoxaluria), or recurrent stone formation despite preventive measures. 2, 3

• Urology referral is indicated for documented stones ≥5 mm unlikely to pass spontaneously or recurrent symptomatic stones requiring intervention 3, 4