A 20 years-old-male patient had sudden onset of weakness losing shortly 2 years back. Now presents with again sudden onset weakness. Investigation of choice is

(B) Edrophonium test > Involvement of two or four limbs distally suggests lower motor neuron or peripheral nerve disease. Acute distal lower limb weakness occurs occasionally from an acute toxic polyneuropathy or cauda equina syndrome. Distal symmetric weakness usually develops over weeks, months, or years and is due to metabolic, toxic, hereditary, degenerative, or inflammatory diseases of peripheral nerves. Drugs that inhibit the enzyme AChE allow ACh to interact repeatedly with the limited number of AChRs, producing improvement in the strength of myasthenic muscles. Edrophonium is used most commonly for diagnostic testing because of the rapid onset (30 s) and short duration (about 5 min) of its effect. An objective endpoint must be selected to evaluate the effect of edrophonium. Examiner should focus on one or more unequivocally weak muscle groups and evaluate their strength objectively For example, weakness of extraocular muscles, impairment of speech, or the length of time that the patient can maintain the arms in forward abduction may be useful measures. An initial dose of 2 mg of edrophonium is given intravenously. If definite improvement occurs, the test is considered positive and is terminated. If there is no change, the patient is given an additional 8 mg intravenously. The dose is administered in two parts because some patients react to edrophonium with unpleasant sideeffects such as nausea, diarrhea, salivation, fasciculations, and rarely with severe symptoms of syncope or bradycardia. Atropine (0.6 mg)should be drawn up in a syringe, ready for intravenous administration if these symptoms become troublesome.