[Malignant melanoma of the pelvis as a possible cause of pelvic limb lameness in two gray mares].

The study describes two cases of grey mares diagnosed with malignant melanoma in the pelvis, which possibly led to chronic pelvic limb lameness and limb abduction during the non-supporting phase of the stride. The melanoma was confirmed via histological examination and post-mortem examination revealed metastases in several organs.

Clinical Findings and Diagnosis

• The research focuses on two grey mares, a 12-year-old Arabian and a 13-year-old Lippizaner cross, that were showing chronic pelvic limb lameness and abduction of the limb during the non supporting phase of the stride. Upon a clinical examination, melanomas were found under the tail and on the perineum, alongside oedema of the proximal lame limb. During rectal palpation, a mass in the pelvic area was detected.
• Laparoscopy was utilized to examine the observed mass in more detail, and a provisional diagnosis of malignant melanoma was made. Histological examination of a biopsy taken from the mass confirmed the initial diagnosis. Postmortem examination then revealed a large black mass in the pelvis and metastases in several organs.
• The study puts forward an hypothesis that the lameness and limb abduction seen in these horses were potentially caused by a combination of factors: pain, a mechanical limitation, and paresis or paralysis.

Implications of the Study

• The research implies that if an older gray horse with melanomas on typically prone sites presents with pelvic limb lameness and limb abduction, a malignant melanoma in the pelvis could be considered as one of the differential diagnoses.
• A rectal examination should be implemented due to its utility in detecting a mass in the pelvic area, as observed in the two studied mares.
• The study also highlights diagnostic laparoscopy in standing horses as a useful approach to confirming the provisional diagnosis of a pelvic malignant melanoma.