What symptom is commonly the first sign of local anesthetic systemic toxicity affecting the CNS?

• A. Headache
• B. Dizziness
• C. Tinnitus or a Metallic Taste
• D. Nausea

Answer: (C)

Metallic taste or tinnitus is commonly the earliest sign of local anesthetic systemic toxicity affecting the CNS. When the anesthetic reaches higher blood levels, it first disrupts neural pathways involved in taste and hearing, producing a sudden metallic sensation or ringing in the ears. These symptoms reflect initial CNS excitation and can appear before more severe signs such as dizziness, agitation, seizures, or loss of consciousness. Other symptoms like headache or nausea are nonspecific and less reliable as early warning signs, and dizziness can follow as CNS involvement progresses. Recognizing a metallic taste or tinnitus promptly allows you to stop the injection, monitor the patient, and initiate LAST management before progression to more serious CNS effects.