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CLINICAL CASE PRESENTATION · January 18th, 2021

Solar Thermal Necrosis: A Case Study on Treatment and Care

by Christine Stencel, DVM

VETERINARIAN

The following report documents a case of severe, solar-induced thermal burns over the dorsal skin of a canine patient after prolonged sunlight exposure in high ambient temperature. The subsequent treatment and care outlined here resulted in a full discharge for continuing home care.

BACKGROUND

A 2½-year-old intact, male, white and black pit bull presented for a six-day history of pain and easily epilated fur on the dorsum.  The owner reports he had been outside for a while the day prior to the onset of symptoms, and thought he had been sunburned. They applied over-the-counter triple antibiotic ointment to the skin but it continued to worsen. The patient is fed a commercial dry diet.  The patient was not up to date on vaccines or routine heartworm testing and received no medications or preventatives.  There were no exposures to caustic agents, there were no topical flea and tick medications applied to the dorsum, and the patient had not been hosed down with a garden hose that had been lying in the sun.

CASE REPORT

Initial Examination

The patient was in too much pain to permit examination, so he was sedated with dexmedetomidine and butorphanol to facilitate a thorough exam. Most of the dorsal thorax was covered by burn wounds, the cranial area had a large eschar that was separating from the surrounding skin and exuding purulent discharge. A sample was collected for culture. There were small areas of red burn wounds over the right lateral shoulder, the dorsal lumbar area, and an area on the right lateral stifle with necrotic skin that was nearly completely separated from the surrounding tissue. The necrotic skin/eschar on the dorsal cranial thorax and the right stifle were debrided and cleansed.  A tie-over bandage was placed over the cranial dorsal thorax, with Microlyte Ag film placed on the wound bed.  Microlyte Ag is a thin film dressing that contains antimicrobial silver and promotes healing.  The patient was discharged on carprofen, gabapentin, and amoxicillin/clavulanate pending culture result.

The following are images from the initial presentation after sedation and initial shaving:

 

Follow-up Examination

The patient returned for a bandage change and recheck 2 days later. Due to reports of constant shaking of his body and scratching at the bandage, the tie-over bandage had been dislodged and was not a good option going forward.  The culture was positive for Staphylococcus aureus which was sensitive to amoxicillin/clavulanate, and for Enterbacter cloacae which was resistant to amoxicillin/clavulanate.  The antibiotic was switched to trimethoprim-sulfa for 10 days based on culture results, although there are some resources that advise against systemic antibiotics for burn wounds and advocate for topical treatment only to reduce the risk of creating antibiotic resistance in the wounds.  He was not cooperative for cleaning or treating of the wounds while awake, but there was no new tissue ready to be debrided yet.  A full torso bandage was applied, with mupirocin on the open wound beds and silver sulfadiazine cream over the rest of the burned tissue.  Silver sulfadiazine cream was avoided on the open wound beds due to reports that it can delay epithelialization.

Extended Care

The patient returned for sedated rechecks and treatments twice weekly for 3 weeks, then once weekly for 2 more weeks.  It can take several weeks after a thermal injury for burns to fully develop. During the first 3 weeks, necrotic skin and eschar were debrided as they developed, and the wounds were cleaned and treated with hydrotherapy. The wounds were initially treated with medical-grade Manuka honey and non-adherent Telfa pads under the full torso bandage until debridement was finished. Then hydrocolloid dressings were used for the final 2 weeks.

The most delayed area to necrose and need full debridement was on the dorsal lumbar area. The lumbar area of a male dog is a difficult area to incorporate into a full torso bandage, so the first attempt at covering it was an adhesive Tegaderm hydrocolloid dressing that was applied to the dorsal lumbar area with no bandaging over it. However, at recheck 3 days later that patch had fallen off on its own and a new bandaging plan was needed.  At that time (the end of the initial 3 week period), the burns had fully developed and all necrotic tissue had been debrided. Tegaderm hydrocolloid dressings were then applied to all open wounds along the dorsum, held in place by the adhesive strip around the edges of these dressings plus several drops of tissue glue.  Cast padding was wrapped around the thorax with a layer of roll cotton laid on the dorsal lumbar area and taped to the cast padding cranially, then tubular stretch bandaging was cut to the length of the patient’s body with 4 leg holes and a hole for the penis and applied to the entire trunk of his body. This helped anchor the cast padding on his thorax as well as anchor the dressing and cotton to his lumbar area.  The thorax was additionally covered with VetWrap as an exterior layer. This bandaging technique stayed in place for him successfully until the next weekly recheck.  The following are images from approximately 2 weeks post-injury:

The following is an image from approximately 3 weeks post-injury after complete debridement:

The following is an image from week 4 after his first week of hydrocolloid dressings being in place. The dressings are excellent at maintaining a moist wound environment, which did lead to some mild self-limiting wound edema.

The following is an image from week 5, after which the patient was discharged to home care with silver sulfadiazine cream and T-shirts. Requests for the owner to send photos of his continued healing progress from home have so far been unsuccessful.

 

Final Assessment

Several adjustments were made to this patient’s treatment plan in regards to dressings and bandage types over time. He was initially treated with Microlyte Ag strips and mupirocin because they were readily available in the clinic at his first visit. He was then transitioned to medical-grade Manuka honey and silver sulfadiazine cream. He was then transitioned to hydrocolloid dressings. There are different benefits to all these types of dressings in regards to reducing infection and enhancing epithelialization, and efforts were made to match the state of the wound to best dressing options. Tie-over bandaging was abandoned in favor of full torso bandaging, with the addition of a full-body tubular bandage component when the lumbar area needed to be incorporated into the bandaging.

Another management issue with this patient is that during the first few weeks after injury, he progressively lost weight (he started at 52.2 pounds, went down to 45.9 pounds).  Patients healing from extensive burns do require higher calorie intake to meet their metabolic demands and can lose protein in their wound exudate.  Once the client was advised to feed substantially higher calories the patient did successfully gain his weight back.

This was the author’s first-time managing burn wounds of this extent.  Upon initial presentation, alternate explanations for the cause of the burns other than sunburn were sought but none found.  The typical clinical thinking regarding sunburns is that they occur only on thinly furred, poorly pigmented areas.  However, as this patient’s burns declared themselves, it became obvious they only affected the darkly pigmented areas of this patient, often following the sharp demarcations of black to white fur transition and the solitary black oval spot on his dorsal lumbar area.  This is a documented phenomenon called solar thermal necrosis. Black skin absorbs almost 50% more solar radiation than white skin.  The hypothesis is that the darkly pigmented skin of these animals acts as a “heat sink” that concentrates solar radiation energy when the animal is exposed to high ambient temperatures.

The weather in Milwaukee at the time of the sun exposure for this patient was very sunny with high temperatures of 90 -95 degrees Fahrenheit.  The exact amount of time this patient spent outside in the sun could not be elicited from the owner, but the impression given upon questioning is that it was a few hours, and he did not seem under any heat stress at the time or later that day. In addition to all the wound care listed above, the owner was instructed not to let him spend any time outdoors during the intense heat of the day, and to utilize UV and sun-blocking garments for him in the future, and to install shade in his yard.

Christine Stencel, DVM

VETERINARIAN

Thiensville-Mequon Small Animal Clinic | Thiensville, WI

Dr. Stencel was born and raised in the Milwaukee area. She is a 2005 graduate of the University of Wisconsin-Madison School of Veterinary Medicine. She returned to the Milwaukee area following veterinary school and has been with the Thiensville-Mequon Small Animal Clinic since then. Dr. Stencel enjoys internal medicine and sees canine, feline, and occasional small mammal patients. She and her husband have two children, one cat, and one dog. In her free time she likes to travel, camp, hike, garden, and read science fiction.

One Response

  1. William Harper says:

    Was toxic epidermal necrolysis considered as a cause and if so, how do you differentiate between the 2?
    Thanks for the case.

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