Any general reduction in vitality and strength of body and mind resulting from a debilitating chronic disease WordNet 3.0 & Open English WordNet

Cachexia is a complex syndrome associated with an underlying illness, causing ongoing muscle loss that is not entirely reversed with nutritional supplementation. Wikipedia

Wasting syndrome Wikidata

The involuntary loss of more than 10 percent of body weight, plus more than 30 days of either diarrhea or weakness and fever. Wasting refers to the loss of muscle mass, although part of the weight loss may also be due to loss of fat. HIV-associated wasting syndrome is considered an AIDS-defining condition. OmegaWiki

A systemic wasting of muscle tissue, with or without loss of fat mass, that accompanies a chronic disease. Wiktionary

Systemic wasting of muscle tissue that accompanies a chronic disease. Wiktionary (translation)