When cachexia from emphysema causes emaciation, what can be done?

Treatment. The goal of controlling dyspnea in patients with severe COPD can help. Using multiple inhalers (both short and long acting), a pde inhibitor (new drug class), plus exercise seems to help the most. However, weight loss due to COPD is a sign of severe illness and end of life planning (if not already done) should be considered strongly.
Limited options. Unfortunately, by this time returning to normal muscle mass and weight is unlikely. High protein supplements may be of some benefit. This reflects the systemic effect of emphysema on every area, not just the lungs. Anticipating weight loss and eating frequent small meals, trying appetite stimulants like Megace (megestrol) early and exercising may prevent cachexia in some cases. Smoking cessation is essential.
Nutritional support. There are many kinds of nutritional support that can be offered so the patient should be seen by their doctor so this can be initiated. But, this typically occurs when the disease is quite advanced and the overall prognosis is often poor at this stage. Nutritional support can still be attempted, though, so see your doctor.