The challenge with diagnosing rare diseases: The ‘zebra’ diagnosis



See also article by Raes et al.

See also article by Mahne et al.

Haemangiosarcoma is uncommon in the horse which makes it somewhat of a diagnostic dilemma because ‘common diseases occur commonly’ leaving haemangiosarcoma off the top list of differential diagnoses in most patients. The case reports by Raes et al. (2014) and Mahne et al. (2014) illustrate nicely 2 clinical presentations of haemangiosarcoma in the horse and the management of these horses despite the challenges with obtaining an antemortem diagnosis.

Haemangiosarcoma occurs most commonly in dogs, particularly German Shepherds and Golden Retrievers and frequently affects the spleen. Dogs ‘classically’ present with cardiovascular collapse and abdominal distention (haemoperitoneum) as a result of haemorrhage from the splenic tumour. Based on the breed and patient presentation, the disease is somewhat readily diagnosed in dogs. Interestingly, the tumour rarely occurs in cats and man.

Being a tumour of vascular endothelial origin, haemangiosarcoma can occur in any tissue. Clinical signs are reflective of the tissues affected as well as the effects of haemorrhage from the tumour. Clinical manifestations can be extremely variable as illustrated by Raes et al. (2014) and Mahne et al. (2014) and range from poor performance to vaginal discharge to fracture or neurological signs (Southwood et al. 2000). The musculoskeletal system is more commonly affected in horses than it is in dogs (Southwood et al. 2000; Johns et al. 2005). All young horses with haemangiosarcoma presented with cutaneous or limb swelling or joint effusion (Johns et al. 2005). The most common presenting complaints in horses with eventual disseminated haemangiosarcoma were dypsnoea (26%), muscular or subcutaneous swelling (24%), epistaxis (17%) and lameness (12%) (Southwood et al. 2000).

There are some ‘classic’ presentations of the disease in horses. One such initial presentation is that of presumed trauma and lameness or large haematoma formation. While a clinician would be accused of considering ‘zebra diagnoses first’ if haemangiosarcoma was on the list of every horse presenting for trauma, there are some clinical features that should be noted and if observed may make haemangiosarcoma (or any other neoplasia) higher on the list of considerations. A thorough history should be obtained and complete physical examination performed on every patient. Clinical awareness and astute observation are critical when evaluating any animal with any presenting complaint. The history and clinical presentation of the patient should make sense when arriving at a diagnosis and when it does not make sense further investigation is required. Observations such as pale or icteric mucous membranes, fever and inappropriate tachycardia or tachypnoea in a patient presenting for apparent trauma or lameness always warrant further investigation. Re-breathing examination, haematology and biochemistry and ultrasonographic evaluation of the lesion site are inexpensive initial diagnostic procedures. Dull lung sounds ausculted during re-breathing examination, distress during re-breathing, or failure to recover within a few breaths should prompt thoracic ultrasonographic (or radiographic) evaluation. Anaemia, neutrophilic leucocytosis, thrombocytopenia and azotaemia have been reported with some frequency in horses with haemangiosarcoma (Southwood et al. 2000; Johns et al. 2005). Sonographic evaluation of the affected area (e.g. haematoma or swelling) often reveals masses (Johns et al. 2005). Biopsy of tissue (if possible) and histological evaluation is useful for diagnosing haemangiosarcoma (Johns et al. 2005). Unfortunately, cytology is usually most consistent with haemorrhage and not particularly useful for diagnosing haemangiosarcoma (Southwood et al. 2000; Johns et al. 2005). Extensive haematoma formation, particularly if it is unresolving or associated with inappropriate haemorrhage when surgically approached, warrants submission of a biopsy sample (if possible). Abdominal ultrasonographic evaluation should be considered in a patient not responding to initial treatment or with apparent systemic disease (e.g. weight loss, inappetence, dull mentation, anaemia and thrombocytopenia). Radiographic evaluation or other musculoskeletal imaging is indicated in certain instances such as that presented by Raes et al. (2014) and Mahne et al. (2014). The key point is that when the patient presentation does not necessarily concur with the most apparent diagnosis other disease processes should be considered prompting further investigation and close monitoring of the disease progression.

Haemangiosarcoma is typically an aggressive tumour (in all species) and is likely to have metastasised by the time of diagnosis making even ‘early aggressive therapy’ unrewarding. Often the site of haemangiosarcoma in the adult horse is not amenable to resection as would have been the circumstance in the horses described by Raes et al. (2014) and Mahne et al. (2014). Early diagnosis is central to preventing unnecessary patient (and client) suffering and client expense associated with futile treatment. In young horses (≤3-years-old); however, the disease may be different. A small number of young horses may resolve spontaneously and, on occasion, early resection of the affected tissue (when possible) in young horses may be successful (Johns et al. 2005).

Author's declaration of interests

No conflicts of interest have been declared.