CAC treatment eliminates the reflux of superficial veins that cause varicose veins by filling targeted veins with CA. CA is a strong, fast-curing adhesive used in industrial, medical, and household applications. It is often used as a nail adhesive in the beauty industry, including nail art.

Various reports of allergic reactions after CAC are recognized.

Morrison et al. found no allergic reactions to the skin or deep tissue in 108 CAC cases.1

On the other hand, there are reports of hypersensitivity reactions to subcutaneous tissue at the time of delivery of the CAC system2 and reports of generalized urticaria one week after CAC3. Park et al. reported an unusual phlebitis-like reaction that occurred in 25% of CAC cases, in which they postulated a type IV hypersensitivity reaction (delayed allergy) as the mechanism4. The above complication is also mentioned in the "Guidelines for Endovascular Therapy with Cyanoacrylate Adhesives for Varicose Veins" in Japan and is called phlebitis, the mechanism of which is still unclear5.

In our case, erythema and swelling appeared on the medial side of the affected thigh seven days after surgery, leading us to suspect a type IV hypersensitivity reaction. A DLST was performed using the CA used in the treatment to clarify this. This test is useful to determine whether a particular drug is involved in drug-induced allergic symptoms, especially liver damage and hematopoietic disorders caused by type IV allergic mechanisms. The sensitivity and specificity of the test are 60-70% and 85%, respectively, depending on the target drug6.

The DLST is more likely to be negative when steroids, antitumor agents, or immunosuppressive agents are used, whereas it may be positive when non-steroidal anti-inflammatory drugs are used. In our case, the patient took antihistamines but no other anti-inflammatory drugs.

As the patient was not taking any medications that could have affected the results when the test was performed, the results were considered highly reliable. Therefore, a positive DLST means indicated a delayed allergy for CA.

Jones et al. stated that they administered oral steroids and antihistamines when a post-CAC hypersensitivity reaction was suspected7. Our patient was treated with a combination of oral antihistamines and steroids and the skin rash disappeared once, but recurred as a generalized rash, including on the face. Furthermore, the rash was a highly pruritic wheal, without erythema, swelling, or pain on the medial side of the affected thigh seen in the acute phase of phlebitis. Jones et al. stated that the incidence of hypersensitivity reactions leading to removing the treated vein is less than 1 in 10,000, according to the manufacturer's publication. Therefore, this case was regarded as such an incident.

The total number of CAC cases at our hospital in the end of December, 2022, was 368. Meanwhile 27 cases doubted an allergic reaction, including extremely slight symptoms, were detected (7.3% during all cases), and all of them were performed DLST for CA. As a result, 3 cases (0.8% during all cases) were detected as positive (more than 180% of S.I. ).

In each DLST-negative cases, redness, swelling and pain on the medial side of the affected thigh occurred 6-8 days after CAC, and the symptoms were improved by the internal use of antihistamines and non-steroidal anti-inflammatory drugs. These cases are considered as phlebitis.

As a breakdown of 3 DLST-positive cases, one case was strong positive S.I. 690%, and the other two cases were S.I. 288% and 237%. Not only a redness, swelling and pain on the medial side of the affected thigh, but also the wheal with the itch were detected with all of these 3 cases. The systemic wheal was found on only the DLST strong positive case. About the DLST slight positive cases, the relief of symptom was detected by the internal use of antihistamines and non-steroidal anti-inflammatory drugs. On the other hand, about the DLST strong positive case, the improvement and stabilization of the symptom were not detected, even if steroids were given. The disease severity varies according to each S.I. value in the DLST-positive case, that mean delayed allergy for CA. The removal of the CA-filled great saphenous vein could be necessary in the case of the abnormal high S.I. value like this case, without the improvement of the symptom only by medication treatment. Thus, it was suggested that DLST could show not only the diagnosis of the delayed allergy, but also the later treatment policy with S.I. value in the positive cases.

In addition, our patient's DLST SI value gradually decreased after removing the CA-filled vein and eventually became negative. This is consistent with the patient's skin symptoms, which also lend credence to the DLST.

Although not a frequent occurrence, it would be ideal to confirm the presence of an allergic reaction to CA before surgery to avoid hypersensitivity reactions after CAC. However, Jones et al. stated no valid evidence exists for a CA patch test routinely performed before CAC surgery7. For this reason, our clinic now asks patients to indicate on the initial medical questionnaire whether or not they have a history of allergy and the nature of their symptoms.

Given the current difficulty in confirming the presence or absence of preoperative hypersensitivity reactions to CA, the DLST for CA may be useful in determining the course of treatment in the event of a postoperative allergic-like reaction.