D3.44 - The Role of Medical History and Diagnostic Testing in Identifying Post-Surgical Allergic Reactions

Reactions, even severe, manifested by a severe bullous or erosive morphology, following contact with iodinated derivatives have been frequently described and attributed to both the irritant nature of these products and the presence of sensitization. Even today, despite the publication of several papers and reviews on the subject, there is still some disagreement on how to distinguish between irritation and sensitisation reactions.

We present the clinical case of a 65-year-old patient evaluated at our Allergy and Clinical Immunologic Unit for post-operative dermatitis. In anamnesis: overweight and hypertension on sartan therapy with good clinical control. In 2010, she was already evaluated for chronic dermatitis in another allergy department, with evidence of sensitisation to disperse blue 124. 

In March 2022, the patient underwent left knee replacement surgery, and a few hours later developed a bullous, intensely pruritic skin reaction. Local treatment was applied, leading to the resolution of the lesions, although a dyschromic skin lesion persisted.

In November 2023, the patient underwent surgery for implantation of the contralateral prosthesis, and a more extensive skin reaction developed a few hours postoperatively. In November 2024, she was admitted to our Unit.  No further surgical procedures were reported. Upon reviewing the medical records, it was noted that povidone-iodine and Chlorhexidine had been used for skin disinfection prior to both surgeries.

Irritant reactions are typically characterized by a burn-like morphology and, when caused by surgical disinfectants, are often located distant from the surgical incision site. However, the recurrence of a similar reaction, in a more extensive form, during the second operation makes an irritant reaction unlikely, suggesting the possibility of a hypersensitivity reaction.

Therefore, we proceeded with patch testing to differentiate between these two types of reactions. Initially, an open patch test with PVP-I (10-1% in aq) and Chlorhexidine was performed, yielding negative results. A subsequent closed patch test with thimerosal and povidone-iodine was positive.

This clinical case underscores the importance of obtaining a detailed medical history in addition to performing diagnostic tests.