Skin Rash in a Stage 4 CKD Patient Treated for Hyperkalemia

Case Description A 63-year-old man whose history was significant for CKD stage 4 (baseline serum creatinine of 3.2 mg/dl) secondary to IgA nephropathy, proven by biopsy specimen at age 39, and chronic recurrent hyperkalemia presented with worsening, bilateral, lower-extremity, nonhealing, ulcerative lesions. Further history revealed that he had been prescribed patiromer, to treat hyperkalemia, 4 weeks before the current presentation. Two weeks after the initiation of patiromer, the patient developed bilateral, lowerextremity, erythematous swelling, accompanied by a painful, petechial rash. Subsequently, the patient was treated with oral antibiotic for a presumed diagnosis of cellulitis. Examination was significant for large, exudative ulcers and purpuric macules associated with weeping edema (Figure 1). Laboratory workup was remarkable for potassium (4.7 mmol/L), BUN (94 mg/dl), creatinine (4.1 mg/dl), and white blood cell count (11.3 cells/mm). Deep venous thrombosis was ruled out via a lower-extremity venous Doppler ultrasound. A complete workup for GN was unremarkable. The wound cultures grew Pseudomonas aeruginosa, which was sensitive to ciprofloxacin. A skin biopsy specimen showed small-vessel vasculitis, with intraepidermal and subepidermal neutrophilic aggregates, and positive direct immunofluorescence for fibrin along luminal blood vessels (Figure 2). No evidence for IgA deposition was noted on immunofluorescence exam. The patient was discharged on high-dose, tapering prednisone and oral ciprofloxacin. The patient had complete resolution of the skin lesions 4 weeks later.