Occult osseous metastasis of a colonic adenocarcinoma visualized with technetium tc 99m hydroxymethylene diphosphate scintigraphy in a horse.

The study reports a case of a five-year-old Arabian horse with occult bone metastasis of colonic adenocarcinoma, revealed through technetium Tc 99m hydroxymethylene diphosphate scintigraphy.

Case Presentation and Initial Findings

• The case at hand involves a 5-year-old Arabian horse that was brought to the vet clinic after suffering from intermittent fever of unknown origin, decreased appetite, drowsiness, and an instance of collapse. All these symptoms were acute, observed only for 5 days prior to the medical consultation.

<liUpon physical examination, the horse exhibited a grade II/VI left-sided systolic cardiac murmur (an abnormal rhythmical repetition of the heart sound) and abdominal splinting. Laboratory analysis indicated the presence of mild chronic inflammation.

• An echocardiogram – or a sonogram of the heart – revealed moderate aortic insufficiency, which means that the horse’s aortic valve wasn’t closing tightly, leading to the backflow of blood.
• Although a single soft tissue opacity was identified in the thoracic radiography, it was not visible on an ultrasound scan. The treatments provided to alleviate the horse’s symptoms did not offer any relief.

Scintigraphy Scans and Final Diagnosis

• Subsequently, nuclear scintigraphy was performed using white blood cells labelled with technetium Tc 99m hexamethylpropyleneamine oxime, but it didn’t reveal any anomalies.
• Another nuclear scan was conducted, this time with technetium Tc 99m hydroxymethylene diphosphate. This diphosphate compound is used to visualise skeletal metabolism and thus, helps in detecting osseous or bone anomalies. It discovered polyostotic disease in the horse, which is a condition characterized by lesions in multiple bones.
• A biopsy of a rib affected by the disease was taken and evaluated. Histopathological examination of the sample showed the presence of disseminated adenocarcinoma, a type of cancer that forms in mucus-secreting glands.

Conclusion and Necropsy Findings

• Given the severe and disseminated cancer, the horse was euthanized. The necropsy and additional pathological examination confirmed the final diagnosis of adenocarcinoma that had originated in the colon.
• It was found that this cancer had undergone osseous metaplasia, a process where normal tissue changes state to bone tissue, and had spread to several organs, muscles, and bones. Thus, the bone disease detected through technetium Tc 99m hydroxymethylene diphosphate scintigraphy was indeed occult osseous metastasis of the colonic adenocarcinoma.