**Core Concept**
Lennox-Gastaut syndrome (LGS) is a severe type of epilepsy characterized by multiple seizure types, including atonic, tonic, and atypical absences. Management of LGS often requires polytherapy with antiepileptic drugs (AEDs) that target specific seizure mechanisms. The primary goal of AED treatment in LGS is to reduce seizure frequency and severity while minimizing side effects.

**Why the Correct Answer is Right**
Lamotrigine is effective in treating LGS due to its broad-spectrum antiepileptic activity. It modulates voltage-gated sodium channels, which reduces neuronal excitability and prevents the propagation of seizure activity. Additionally, lamotrigine has a dual inhibitory effect on excitatory neurotransmission via glutamate release and a facilitatory effect on inhibitory neurotransmission via GABA release. This balanced mechanism contributes to its effectiveness in reducing seizure frequency in LGS patients.

**Why Each Wrong Option is Incorrect**
**Option B:** Gabapentin is primarily used for partial seizures and neuropathic pain; it lacks the efficacy demonstrated by lamotrigine in treating LGS.
**Option C:** Tiagabine is a GABA reuptake inhibitor, which might exacerbate seizures in LGS due to its narrow therapeutic index and potential for increasing seizure activity.
**Option D:** Primidone is an older AED with a broad spectrum of activity, but it is not typically used as a first-line treatment for LGS and can have significant side effects.

**Clinical Pearl / High-Yield Fact**
Lamotrigine is often initiated at a low dose and gradually titrated upward to minimize the risk of severe rash, a well-known side effect of this medication. Close monitoring of patients for signs of rash and adjusting the dose accordingly is crucial to ensure safe and effective treatment.

**✓ Correct Answer: A. Lamotrigine**