Too often, people with PD are assumed to be depressed because they show some of the major symptoms of depression - slowness, lack of initiative, excessive sleeping, appetite loss and social withdrawal. But these are also symptoms of PD. The one difference is sadness. People who have PD are not necessarily sad, so if your husband is feeling sad, that may be a tip-off that he is depressed.
Ask your husband's neurologist to arrange for a diagnostic evaluation for depression. Neurologists or neuropsychologists perform these tests. If he is depressed, counseling therapy or medications may be considered.
If it is erroneously assumed that PD is causing his symptoms, and he is put on a higher dosage of PD medication, his depression is not going to lift. On the other hand, people with PD who are depressed do respond to antidepressants. There are many from which to choose. The treatment should be tailored to your husband, who should then be closely monitored to ensure the medication is effective.