The following case study was used by Andrew J. White, MD, the James P. Keating, MD Professor of Pediatrics and division director of pediatric rheumatology, Washington University School of Medicine, and director of the St. Louis Children’s Pediatric Residency Program, as part of the “Patient of the Week” (POW) series. Many of the POW case studies cover uncommon illnesses, or common illnesses with unusual presentations. If you would like to be added to the POW email distribution, send an email to [email protected]

CC: 12 yo boy with a rash on his right leg for 3 months.

HPI: The rash began without preceding trauma or illness. It Leg rashis not pruritic, painful, swollen, or raised. It is pinkish-red and has not changed in color but it is growing in size. He has never had anything like this before and has no rash on other parts of his body. He has not been applying any treatment or creams to the rash. He has had joint pain in the last few years and was diagnosed with both Sever's and Osgood-Schlatter, but this is improving and he now has only minimal intermittent knee pain after prolonged activity. He has no heel pain. He has not had fevers, weight loss, joint swelling, alopecia, oral ulcers, GI symptoms, Raynaud's, epistaxis or difficulty urinating. 
He plays video games for hours in the basement with a nearby space heater to keep warm. The heater is located near his right leg.


  • Immunizations are up to date
  • Never been hospitalized or had surgery.
  • Osgood Schlatter 
  • Sever's disease
  • ADHD

SH: Lives with parents and sister. He has 2 dogs and a rabbit. 7th grade, he plays in the band.
Family History: No one with rheumatoid arthritis, ankylosing spondylitis, Scleroderma, Sjogren's, dermatomyositis, vasculitis, SLE, psoriasis, thyroid disease, or IBD.
Physical Exam:

  • Height is 161.3 cm and weight is 51.6 kg 
  • Temperature is 36.7 °C (98.1 °F) 
  • Blood pressure is 110/74 and his pulse is 78 
  • Respiratory rate is 16 and oxygen saturation is 97%  
  • General: no distress, well appearing, growth appropriate for age
  • HEENT: pupils equal, round, reactive to light, sclera and conjunctiva noninjected, oropharynx without erythema, ulceration or exudate and mucous membranes moist
  • Neck: normal range of motion, no masses
  • Lymph: no lymphadenopathy
  • Lungs:  clear to auscultation, no wheezes or rales and un-labored breathing
  • Cardiac: there are no murmurs, rubs, or gallops
  • Abdomen: normal bowel sounds, soft, non-distended, no mass, no organomegaly
  • Skin: there is a blanching reticulated area of erythema on the lateral aspect of the right leg. The left leg has no rash. No nailfold telangiectases, no nail pits or ridging, no digital ulcerations, normal capillary refill and no sclerodactyly. 
  • Neuro: normal affect and cranial nerves intact, 2+ reflexes at knees
  • Musculoskeletal: full range of motion of all joints without tenderness, erythema, warmth or effusion

Diagnosis: Erythema Ab Igne (ICD 10 L-59.0)

The exposure to a heater near his right leg makes this presentation is most consistent with erythema ab igne. This is an asymptomatic cutaneous disorder resulting from chronic exposure to infrared radiation in the form of heat.

The treatment involves removing the heat source. Hyperpigmentation may occur but will typically fade over months. Other diagnoses to be considered include livedo reticularis, which is typically symmetric/bilateral on the extremities, is reversible, not fixed, and is particularly noticeable with cold exposure. Livedo racemosa is a mottled, irregular hyperpigmentation that is fixed and partially blanchable. It is typically a violaceous, broken reticulated pattern and can be associated with underlying systemic disease.

This patient is well-appearing and has no associated symptoms to suggest systemic autoimmunity or vasculitis, thus the most likely diagnosis is erythema ab igne.

To learn more about this case study or to speak with Dr. White, email [email protected]