TDK conference 2019

Melarsomine (Immiticide inj.; Merial, France) is used intramuscularly against adult heartworms when treating canine heartworm disease. It is highly irritative, therefore owners and even veterinarians often have fears to apply it. The drug should be injected into the paralumbar muscles which are thick enough and have a good blood supply providing proper absorption. Little is known how to determine precisely the optimal location of the injection needle. As to our preliminary experience, ultrasonography seemed to be useful to aid the injection technique. This has not been published before and its anatomical background was even not known.In the anatomical part of our study, we dissected the epaxial lumbar muscles layer by layer to become familiar with these less frequently examined structures. We also prepared the muscles, vessels and nerves in details, providing a guide for understanding the anatomy of the region for veterinarians. Then, we injected „SILORUB DS F-TG“, a double component silicone-gum with different dilutions to simulate the distribution of melarsomine within the paralumbar muscles. This material has higher consistency than melarsomine, therefore we diluted it even more as recommended by the manufacturer. Diluted methylene blue solution was also injected in other cadavers for tracing and demonstrating the further spreading of this fluid.In a cadaver, ultrasonographic (US) appearance of the paralumbar muscles was studied and their thickness was measured. Then, dilated methylene blue was injected with ultrasound guidance. In one living dog with HWD and treated with melarsomine, the injection process together with simultaneous ultrasonography was recorded by video-imaging to follow the location, distribution and absorption of the drug.As a results of our dissection study we demonstrated the nerve fibres of the dorsal branches from the lumbar plexus clearly segmented in this particular region and were not in contact with the injected materials. SILORUB DS F-TG and methylene blue were well distributed inside the lateral epaxial system. As to the shape and volume of the injected silicone material, it depicted the ‘first minute’ phase of the distribution precisely. The further path of the injected material was seen in the methylene blue studies better because of the thinner dilution.During the video-recorded injection process, melarsomine was not fully gravitating, but its majority was spreading along the thickest fascia of the musculature. Three minutes thereafter, no US signs of the melarsomine solution were seen, suggesting a full absorption, at least macroscopically.

Our detailed anatomical description can aid the correct in vivo injection technique and assures veterinarians that no severe neurological complications might occur when applying melarsomine as prescribed. The topographic anatomical and US findings were in accordance. Ultrasonography can be a useful tool to determine the optimal location of the injection site of melarsomine.