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Thanks for contacting with your health concern
1. since he is a diagnosed case of ALS and under 
Neurologist and Primary Doctor supervision who have ordered the relevant investigation and medications for this problem [edema] thus they are well aware of patient's health condition and prognosis, thus without commenting on the medications, I'm of the following opinion till you get an appointment:
i. Physical examination is of utmost importance since swelling could be due to edema, allergic inflammation or infection, for that certain investigation like 
complete blood count, liver and 
kidney function test, heart 
ultrasound, total proteins in body and 
thyroid profile, abdominal or pelvic CT imaging to rule out any growth causing venous compromise, have to be done.
ii. It could be a blood clot which can lead to edema due to obstruction to blood flow leading to increased hydrostatic pressure in the venous system and causing swelling. 
PS. A Doppler study or D- dimer test can confirm it, but common causes should be ruled out first.
iii. Once the cause is removed the swelling will automatically subside.