Loss of appetite is one of the symptoms of depression.
Various causes can be considered for loss of appetite in the elderly.
拒食症 specifically refers to the eating disorder anorexia nervosa, whereas 無食欲 describes the symptom of appetite loss itself, which can have many causes.
anorexia nervosa
Compound of 無 (mu, 'without') + 食欲 (shokuyoku, 'appetite'). The reading むしょくよく follows standard on'yomi.