We report a 40-year-old man who has Marfan's syndrome and was recently diagnosed to have pulmonary tuberculosis when he presented with chronic cough. He was admitted with bilateral lower limb weakness which was ascending in nature. He eventually required ventilation. It was initially thought to be isoniazid-neuropathy. However, stopping the drug did not improve the condition and the patient developed bilateral lower motor neuron 7th cranial nerve palsy. Nerve conduction, MRI and CSF studies were done to confirm a first case report of AMSAN variant progressing to CIDP in a patient with Marfan's syndrome and pulmonary tuberculosis.