What's your diagnosis? Dyspnea and Porphyria in Rats

Our veterinary staff received a male 375-g Wistar rat in severe respiratory distress. On the previous day the rat had undergone surgery. An experienced research technologist, who had completed the identical procedure successfully in the past, did the surgery. He had anesthetized the rat with pentobarbital, 42 mg/kg intraperitoneally (i.p.) and did not require a second dose for adequate maintenance of anesthesia. Completion of the surgical procedure required approximately 60 minutes. Using aseptic technique, the research technologist placed a silicone implant subcutaneously in the right inguinal region and sutured it to the abdominal wall to prevent migration. After the surgery, he gave the rat a subcutaneous (s.c.) injection of buprenorphine (0.08 mg/kg) and returned him to his cage. When checked the next morning, the rat was salivating and had some bedding stuck to the area around his mouth. Approximately 36 hours after surgery, the rat was dyspneic and appeared to be choking. He was breathing heavily through his mouth and was salivating excessively, causing bedding to become matted around his mouth (Fig. 1). Porphyrin staining was present around the rat's eyes and on his front feet (Fig. 1).

Figure 1

Porphyria in a dyspneic rat.

Consequently, we decided to euthanize the rat. The research technician who euthanized the rat and removed the implant noted no obvious complications associated with the surgery. Veterinary staff did a necropsy immediately after euthanasia and found the esophagus to be grossly distended and strawlike in color (Fig. 2). The distension and discoloration extended from the cardiac orifice of the stomach to the cranial aspect of the thorax. The stomach was full and appeared larger than normal (Fig. 2), and the intestines were distended from gas with a small amount of fecal matter present. Esophageal and gastric contents were straw-colored, fibrous, compacted, dry, and crumbly upon manipulation (Fig. 3). Almost no food was present in the stomach. We did not see lesions in any other organs: the lungs were pink, the trachea was clear of any apparent obstruction or damage, the heart was unremarkable, and the thoracic cavity was free of fluid.

Figure 2

Gastric and esophageal distension in a rat.

Figure 3

Esophageal and gastric impaction in a rat.

Several days later, another rat presented with history and clinical signs similar to those of the first rat. We also euthanized and necropsied this rat, and found similar lesions. We had maintained both rats on ad libitum food and water before and after surgery and housed them in polycarbonate cages with hardwood bedding.

Based on the surgical history of these rats, what could cause clinical and necropsy signs such as these?

What's your diagnosis?