Heating pad blotches now have a name -- erythema ab igne

Erythema ab igne. Do not ask me how to pronounce it, but typing it into google images will show you the all too common images ICers see on a daily basis on their inner thighs due to heating pad usage. However, the ones covering the entire leg likely was caused by something other than just a heating pad.

"A middle-aged man presented with intractable abdominal pain from chronic pancreatitis secondary to excessive alcohol use in the past. The pain was unrelieved by thoracoscopic splanchnicectomy and regular opioid analgesia, and he had been using a hot water bottle for years to obtain relief.
The reticular, nonblanching hyperpigmented discolouration of the skin is characteristic of erythema ab igne (Figure 1). This is a useful diagnostic sign in pancreatitis,1 but may also be encountered in patients with abdominal neoplasms such as gastric and hepatic tumours.2
It can occur at any site exposed repetitively to infrared radiation in the form of non-painful heat, such as the shins of old people who sit in front of fireplaces in temperate climates or the abdomen and thighs of kangri (a small portable earthen firepot) users in the Himalayas.3
Erythema ab igne is not always an innocuous cutaneous feature as the mitogenic effects of heat can lead to thermal keratoses and skin cancers; mainly squamous cell carcinomas." -- (http://journal.nzma.org.nz/journal/121-1276/3124/)

Evidently it can cause cancer. But, eh, not like we have much of a choice. This fellow had bad stomach pains. This is how you know your patient isn't faking it.