One remarkable clinical pearl I learned comes from a phenomenal clinician, G. Watson James, MD, from what was then called the Medical College of Virginia, currently the Virginia Commonwealth University School of Medicine. It is a physical exam finding made just by observation, perhaps as one enters an exam room. I love those types of pearls of observation, which I call “diagnosis at 10 paces.” Many, many times I've observed bilateral wasting of the muscles of the temples. It's key for me, because it suggests some significant ongoing condition, with the big three Dr. Watson taught me being cancer, tuberculosis, or chronic infection. There was a time in the 1990s and 2000s when AIDS was commonly in that differential as well.
You can also use bitemporal wasting to help make diagnoses of connective tissue disease, rheumatoid arthritis, or malnutrition. Other conditions such as congestive heart failure, COPD, chronic kidney disease, Crohn's disease, mercury poisoning, or trypanosomiasis, which is extremely rare in the United States, also manifest the finding.
Temporal wasting, in the setting of significant pathology and cachexia, is manifested by temporalis muscle wasting, such that the normal fullness of these muscles is absent. Because of the muscle atrophy, the zygomatic bone, the zygomatic arch, and the temporal lines (temporal line of the frontal bone, and the superior temporal line of the parietal bone) are seen quite prominently. Simple adipose scarcity in this same area, as would be the case in thin, fit people, lacks the same appearance and in those folks, one would still notice the temporalis muscles full and contracting with mastication.
It's important to know that there's an inflammatory component to bitemporal wasting. The temporalis muscle is atrophied, so you can actually see fatty degeneration of the temporalis on MRI. Unilateral wasting may be from nerve damage caused by trauma or surgery. In addition to seeing it on MRI, you can actually observe it and measure it accurately with ultrasound. We, primary care physicians, can use portable ultrasound and, interestingly, the size of the temporal muscle correlates with a person's nutritional status and can even predict life expectancy in certain types of cancers.
The inflammation that occurs with some of the diseases that cause bitemporal wasting is mediated by cytokines like tumor necrosis factor, IL-6, and interferon-gamma. Also, leptin levels are increased in inflammation, which in turn decreases your desire to eat because of neuropeptide Y blockade.
I can recall a woman in her 80s with a rectovaginal fistula caused by cancer. She was brought in by her daughter and a son-in-law who demanded to be present at the exam. She came back a week later in terrible pain. She was given more pain medicine, and she returned a week later still in terrible pain. This is when I got involved.
I saw that she had classic bitemporal wasting from her cancer, but I also came to find out that she was malnourished. They weren't providing her with food, and she was in a lot of pain because the son-in-law was taking all her pain medicines, selling them on the streets, and using them himself. We got adult protective services involved. But this lady actually had two things that would have caused bitemporal muscle wasting, which were the cachexia of cancer and also the loss of adipose tissue, which was happening with malnutrition.