Discussion
Betadine is a topical antimicrobial agent with a large iodine content frequently used for wound care. Excessive iodine intake has well-characterized toxicities within the body. Specifically, elevated serum levels of iodine may lead to thyroid dysfunction resulting in both psychological and metabolic effects. In this patient, iodine likely permeated tissues during wound care therein entering the meninges. Furthermore, iodine absorption is enhanced on denuded skin or other tissues without a protective barrier. 5 Every milliliter of betadine 10% contains 10 mg of iodine. Once iodine is absorbed, it reaches equilibrium rapidly with the extracellular space and distributes evenly except in certain areas, one of which is the thyroid where it is used to make thyroxine (T4) and triiodothyronine (T3). Excessive iodine may result in a transient reduction in thyroid hormone synthesis (Wolff-Chaikoff effect) by inhibiting thyroid peroxidase (TPO) activity.6 Iodine also prevents the release of preformed thyroid hormones (called the Plummer effect) by inhibiting proteolysis of thyroglobulin.6 Upon checking her thyroid status, she was found to have a low normal TSH at 0.44 (0.3 – 4.2) and a low normal FT4 at 1.1 (0.9 – 1.7).
A reduction in thyroid hormone influences other organs, such as the pancreas and the brain. In the pancreas, it may lead to decreased insulin secretion, via decreased stimulatory signal on pancreatic beta cells, thus leading to hyperglycemia and worsening of diabetes.7 In the brain, reduced thyroid hormones may result in pseudo-depression due to alterations in metabolic activity of neurons. 8 Thinking back at our patient’s initial presentation to her PCP, we suspect that the systemic absorption of iodine from betadine was exacerbating her chronic medical conditions leading to her worsening mood and diabetes despite taking her medications as prescribed. Given that the half-life of iodine is about 66 days, we theorize that her actual plasma iodine level was much higher.
Given the lack of significant differences seen on imaging as well as her benign physical exam and lab results, we suspected that the patient had a chronic sterile cerebritis due to the Betadine used in wound cares and an acute soft tissue infection of the scalp. We theorized that the irritation seen on imaging resulted from Betadine exposure via seepage thru the cranial mesh fenestration. To confirm this theory, a serum iodine level was obtained which returned elevated at 404 (normal: 40 – 92). Unfortunately, we were unable to obtain an iodine level from the CSF as no such test exists.
During her hospital course, her creatinine improved with intravenous fluids and was determined to be secondary to dehydration from poorly controlled diabetes. She declined any additional procedures to close the defect. Despite being on broad spectrum antibiotics, she began to experience new episodes of confusion. Repeat imaging revealed new enhancement of the scalp overlying the craniectomy defect as well as extra-axial abscess formation, concerning for a worsening scalp infection with involvement of the mesh. The patient was ultimately discharged home on hospice with empiric oral antibiotics for the scalp soft tissue infection and new wound care instructions (using Vashe moistened sterile gauze rather than betadine to avoid worsening of condition).