D2.51 - Contact dermatitis due to continuous glucose monitoring sensors: limitations of standard patch testing

Allergic contact dermatitis associated with continuous glucose monitoring (CGM) sensors is increasingly reported with the growing use of these devices in diabetes management. Reactions typically occur at the sensor application site, ranging from mild erythema to severe eczematous lesions, affecting device adherence and quality of life. Several allergens have been implicated, including acrylates (e.g., isobornyl acrylate and N,N-dimethylacrylamide), colophony and its derivatives, isocyanates, butylated hydroxytoluene (BHT), and, less frequently, salicylates and cyanoacrylates. Standard patch testing often fails to identify the responsible allergens, as many are not included in baseline series, and manufacturers rarely disclose the full adhesive compositions, complicating diagnosis.

We present the case of a 39-year-old woman with type 1 diabetes who developed erythema and pruritus around a FreeStyle Libre® sensor shortly after placement. The sensor was removed, and a Dexcom One+® sensor was placed without issues. The patient had prior reactions to other adhesives and occasionally to artificial nails.

Epicutaneous testing was performed using the TRUE TEST® battery, a dental methacrylate/adhesives battery, and a set for artificial nails for acrylates. 

Epicutaneous tests were negative, with readings at 48, 72 and 96 hours. Following these results, a diagnostic re-challenge was performed by re-applying the FreeStyle Libre® sensor, leading to recurrence of pruritus at the application site approximately 24 hours later. 

We present a case of CGM-related contact dermatitis in which conventional patch testing was negative. However, the tested panels did not include all the allergens found in glucose monitoring sensors.

The recurrence of symptoms upon re-exposure to the FreeStyle Libre® sensor supports an allergic rather than irritant mechanism, emphasizing the need for clinician awareness and targeted allergen testing to improve diagnostic accuracy and patient care.