**Core Concept**
Guillain-Barre syndrome (GBS) is an autoimmune disorder where the immune system mistakenly attacks the myelin sheath surrounding peripheral nerve axons, leading to demyelination and subsequent muscle weakness. The primary goal of treatment is to prevent further nerve damage and support the recovery process.

**Why the Correct Answer is Right**
The first-line treatment for GBS is intravenous immunoglobulin (IVIG), which is believed to modulate the immune response by neutralizing pathogenic antibodies and reducing inflammation. This approach helps to slow down the progression of the disease and promote nerve regeneration. Plasma exchange (plasmapheresis) is another treatment option that involves removing plasma from the blood and replacing it with donor plasma or a substitute solution. This method can also help to reduce the levels of pathogenic antibodies and alleviate symptoms.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because corticosteroids are not the primary treatment for GBS. While they may be used in some cases, their effectiveness in GBS is limited, and they are not recommended as a first-line treatment.
**Option B:** This option is incorrect because antiviral medications are not effective in treating GBS. The syndrome is an autoimmune disorder, not a viral infection, and antiviral medications do not address the underlying pathophysiology.
**Option C:** This option is incorrect because physical therapy is an important aspect of rehabilitation for patients with GBS, but it is not a treatment for the underlying condition. Physical therapy can help patients maintain muscle strength and mobility, but it does not address the autoimmune response that is causing the disease.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of GBS is the rapid progression of symptoms, often over the course of hours or days. Patients may experience muscle weakness, numbness, or tingling in the extremities, which can progress to respiratory failure if left untreated.

**Correct Answer: A. Corticosteroids are not the primary treatment for GBS.