Page 110 - The Netter Collection of Medical Illustrations - Integumentary System_ Volume 4 ( PDFDrive )

Plate 4-25 Integumentary System

The abdomen, lower back,
and legs are most frequently
affected.

ERYTHEMA AB IGNE

Erythema ab igne is an unusual rash that can develop
secondary to exposure to an exogenous heat source.
The name is derived from the Latin phrase meaning
“redness from the fire.” It has a clinically characteristic
pattern. The differential diagnosis is limited. For
unknown reasons, not all persons exposed to heat
sources develop the rash of erythema ab igne. Many
patients develop the rash without even knowing of its
existence. Reported causes have included hot water
bottles, heating blankets, heaters, and computer laptops.
Essentially any exogenous heat source can cause this
reaction. Erythema ab igne has also been called the
“roasted skin” or “toasted skin” syndrome. The exact Also known as “toasted skin syndrome,” erythema
temperature needed for the reaction to occur is ab igne is caused by excessive heat transfer to the
unknown, and for some reason it does not occur from underlying skin. Hot water bottles and heating
hot tub use, most likely because the causes of erythema pads are most commonly implicated.
ab igne are dry heat or temperatures higher than those
of most hot tubs.
Clinical Findings: This condition can be seen in
individuals of any race and gender. The initiating factor
is an exogenous heat source that is applied to the skin.
The heat source exposure is typically chronic and repet- Common Etiologies of Erythema Ab Igne
itive. Patients often notice a fine, lacy, red, reticulated
macule or patch. Occasionally, no inflammatory phase Heating blanket/pad
is noticed, only a reticulated hyperpigmentation of the Hot water bottles
skin. Some patients do not realize that the rash is Localized heaters/radiators
located on skin in direct approximation to a heat source. Laptop computers
The lower back is a commonly affected area, secondary
to the use of heating blankets or bottles to help treat
chronic lower back pain. There have been many reports
of erythema ab igne from exposures to all sorts of heat
sources. Laptop computers can release a large amount
of energy as infrared radiation; if someone is chroni-
cally using a laptop computer in direct approximation
to their skin (e.g., anterior thighs), the rash of erythema
ab igne may develop. The diagnosis is typically made
by clinical examination and historical information.
Patients often need to be asked whether they have been
using a heating device or consistently using a laptop
computer, because the correlation is not evident to temperatures. More frequent exposures and longer Treatment: The goal of therapy is to discover and
them. The development of actinic keratosis or squa- exposures seem to increase the risk of development of remove the exogenous heat source. Once the heat
mous cell carcinoma within the areas of erythema ab erythema ab igne. The exact mechanism by which the source is removed, most of these rashes slowly fade
igne has rarely been reported. rash develops is unknown. away over months. Some of the hyperpigmented areas
Pathogenesis: Erythema ab igne is caused by the Histology: The skin may be slightly atrophic, and may persist, however. Use of emollient creams or Klig-
direct effects of heat on the skin. The temperature elastotic tissue is seen within the dermis. The rete man’s formulation has been reported. Kligman’s formu-
required has not been precisely defined, but the range ridges may be thinned. Some areas may show evidence lation includes a retinoid, a steroid, and a skin-lightening
of 43°C to 47°C seems to be most likely. In any case, of changes such as those seen in actinic keratosis. Vacu- cream. Laser therapy has also been used to decrease the
there must be repeated exposure to subthermal burning olar degeneration of the basal layer can be seen. pigmentary disturbance.

96 THE NETTER COLLECTION OF MEDICAL ILLUSTRATIONS