25 year old male noticed progressive weakness of both lower limbs mainly in the proximal region following an episode of acute gastroenteritis. He was admitted in a teiary care centre on the same day. Weakness later progressed and involved the both upper limbs. During clinical examination, the physician noticed, bilateral LMN type facial nerve involvement, weakness of all the four limbs with grade 1 power, absent deep tendon reflexes and flexor plantar response. As he developed difficulty in breathing, he was suppoed with a ventilator. He remained fully conscious during these days and bowel and bladder function was intact. What would be the first differential diagnosis in this scenario?