A contrasting diagnosis: iododerma

ABSTRACT

An 86-year-old woman presented to the emergency department with acute shortness of breath. She was treated with intravenous furosemide for acute-on-chronic heart failure. Her past medical history included atrial fibrillation, hypertension, diverticulosis and hypothyroidism. Rivaroxaban and levothyroxine were her only long-term medications. On day 5 of hospital admission, she developed painful haemorrhagic and purulent bullae on her dorsal hands, head and neck. These evolved to large suppurative, vegetative plaques over a 72 h period and she developed additional lesions on her trunk, upper back and thighs. The patient had routine blood tests, which showed a raised C-reactive protein at 260 mg L-1, and an acute kidney injury with a glomerular filtration rate of 54 mL-1 min-1. She had a negative COVID-19 swab, and swabs from the lesions for bacterial culture and viral polymerase chain reaction were negative. She had a normal serum protein electrophoresis, immunoglobulin, antinuclear antibody and antineutrophil cytoplasmic antibody. She had computed tomography of her chest 24 h prior to the onset of her lesions, which showed mild bilateral pleural effusions in keeping with fluid overload secondary to heart failure. A biopsy taken from her hand showed orthokeratosis and parakeratosis, and there was bulla formation subepidermally. There was a dense neutrophilic infiltrate with microabscess formation with scattered eosinophils and lymphocytes. There was no evidence of vasculitis. Direct immunofluorescence was negative and a tissue culture for atypical mycobacteria was negative. The patient was commenced on high-dose intravenous methylprednisolone at 500 mg for 3 days followed by 40 mg prednisolone orally for 1 week, but there was a limited response. Our initial differential was Sweet syndrome or pyoderma vegetans;however, the patient had no fevers and no risk factors (malignancy, inflammatory disease, infection, etc.). She also had no response to high-dose oral prednisolone. Given the timing of her CT examination in relation to her acute dermatosis and the use of radioiodine for contrast, we assessed the patient's serum iodine and urine iodine. These were both high at 1.02 mmol L-1 (reference interval 0.32- 0.63) and 3.46 mmol L-1 (reference interval 0.0-2.43), respectively. A diagnosis of iododerma was made. The patient's eruption slowly resolved and at 12 weeks there was evidence of postinflammatory skin changes only. Her urine and serum iodine were rechecked, and both had normalized. In the last 20 years there have been approximately 20 case reports of iododerma. Most have been following iodine contrast use in patients with abnormal kidney function, like our patient. Most describe an acneiform eruption that subsequently evolves to vegetative plaques (Chalela JG, Aguilar L. Iododerma from contrast material. N Engl J Med 2016;374 2477). Iododerma is largely a diagnosis of exclusion, but histopathology and urine and serum iodine levels can help support diagnosis.