I. Introduction
Local anesthetics are injectable drugs frequently used in clinical dentistry[1]. Since the anesthetic effect of cocaine was first discovered in 1884, these drugs have been extensively used, and true hypersensitivity to local anesthetics is very rare[2].
The molecular structure of local anesthetics comprises a lipophilic aromatic ring and a tertiary amine with an intermediate linkage[3]. Anesthetics are classified as either ester- or amide-type local anesthetics based on this intermediate linkage[4]. Differences in chemical structures affect drug duration, efficacy, and toxicity[2]. Para-aminobenzoic acid is a metabolite from ester-type local anesthetics that can induce hypersensitivity. Conversely, metabolites from amide-type local anesthetics are less likely to induce hypersensitivity[5].
The present case involved a patient who presented with delayed swelling of the lower lip after receiving cavity treatment under local anesthesia with lidocaine. He was diagnosed with hypersensitivity to lidocaine. We report the case and discuss appropriate measures for preventing and treating patients with hypersensitivity.
II. Case Report
A 26-month-old boy visited at the Department of Pediatric Dentistry, Wonkwang University Dental Hospital with a cavity in primary molar teeth. His medical, familial and dental histories were unremarkable. Clinical and radiographic examinations revealed the presence of occlusal caries bilaterally in the lower first primary molars (Fig. 1). Considering the patient's age, we decided to proceed with treatment under oral sedation. Approximately 1 hour before initiating the treatment, the patient was orally administered 900 mg chloral hydrate (Pocral®, Hanlim) and 20 mg hydroxyzine (Ucerax®, UBC). The mucobuccal folds of both lower first primary molars were injected with 0.6 mL of 2% lidocaine hydrochloride with 1 : 100,000 epinephrine (2% Lidocaine HCl · Epinephrine Inj., Yuhan). The right lower first primary molar was restored with resin after indirect pulp capping, while the left lower first primary molar was restored with a glass ionomer. The patient’s condition was checked after treatment and before he returned home.
After returning home, the patient presented to the emergency room at Wonkwang University Dental Hospital due to lower lip edema (Fig. 2). After explaining the possibility of lidocaine hypersensitivity to his parents, the patient was moved to an emergency room at Wonkwang University Medical Hospital. Clinical examination revealed localized swelling and pain at the injection site in the absence of other symptoms such as fever, headache, or difficulty breathing.
With his parent's signed permission, a skin prick test (SPT) was administered using lidocaine. SPT results were read after 15 minutes and were positive (Fig. 3). The dermatologist diagnosed the patient with angioedema due to a hypersensitivity to lidocaine. An intramuscular injection of an anti-histamine and a steroid were administered, and the patient was prescribed oral anti-histamines.
III. Discussion
True hypersensitivity to local anesthetics is very rare, accounting for less than 1% of adverse events caused by local anesthetics[6]. However, some patients complain of symptoms similar to hypersensitivity after local anesthesia. Adverse reactions that may be mistaken for hypersensitivity include syncope, panic attack, and toxic effects; therefore, it is important to identify the cause of the symptoms in these cases[7].
In the case of local anesthetic hypersensitivity, it is possible that other constituents in the injection solution besides the active drug could have caused the reaction. Allergic responses also can be due to preservatives or antioxidants in the injection solution[8], as well as latex from gloves, rubber dams, or rubber bungs of the cartridge[9]. However, most adverse reactions associated with local anesthetics during dental treatment are psychogenic. The most common psychogenic reaction is syncope, which can be accompanied by a panic attack, hyperventilation, nausea, vomiting, or heart rate or blood pressure alterations[10]. In addition, a high concentration of local anesthetic in systemic circulation due to repeated injections, accidental intravascular injection, or overdose can cause toxic reactions[2,11].
In the present case, the hypersensitivity reaction was not attributed to latex because a rubber dam was not used during treatment, and there was no evidence of hypersensitivity when latex gloves were used during oral examinations. In addition, the sedative dose was based on the patient's weight, and the dosage of lidocaine was appropriate. A systemic toxic reaction to local anesthetics or other medications was not considered because there were no signs of other systemic symptoms.
Becker and Kenneth[3] summarized the management of patients allergic to local anesthetics using a flowchart. First, the patient’s past medical and dental history should be investigated. Next, common reactions should be ruled out based on symptoms, to distinguish hypersensitivity from syncope or tachycardia caused by epinephrine. If the reaction involves a rash, pruritus, urticaria, or dyspnea, the patient can be diagnosed with hypersensitivity. If the patient knows which drug is causing the hypersensitivity, an alternative drug should be selected. However, if the drug is unknown, an allergist should be consulted for testing. In particular, it is recommended that patients are referred to an allergist for assessment of reactions to frequently used anesthetics, such as lidocaine and benzocaine, as well as sulfite preservatives.
These principles are basic approaches, but patient history is not often useful in pediatric dentistry. In many cases, patients have not previously visited a pediatric dentist, or have no experience with local anesthesia. Similar to the patient in the present case, it is possible to be unaware of a hypersensitivity to local anesthetics, and symptoms could appear during or immediately after the treatment. If symptoms suggestive of a true hypersensitivity occur, the patient should be given immediate treatment. Hypersensitivity to local anesthetics can range from mild to severe. Mild skin response can be managed with oral or intramuscular anti-histamine. A rapid allergic reaction should alert clinicians to a possible anaphylactic response. If acute signs of an anaphylactic response occur, basic life support, intramuscular or subcutaneous epinephrine, and transportation to the emergency room may be required[12].
Patients diagnosed with hypersensitivity to lidocaine should be referred for further investigation to confirm the allergen[13]. Results of allergy testing will identify a specific local anesthetic that can be used for dental anesthesia[12]. During the treatment, the clinician should treat all patients carefully with reassurance to relieve fear and anxiety, use an aspirating syringe, inject slowly, and monitor any adverse reactions[13].