Lymphangiectasia

Description

Lymphangiectasia is a disease of the intestinal lymphatic vessels that results in the leakage of protein rich lymph leaks into the intestinal lumen, producing a protein-losing enteropathy(PLE) and severe lipid malabsorption.

Lymphangiectasia can be classified into a primary or a secondary disease. Primary lymphangiectasia usually only affects the intestine but it occasionally involve a concurrent chylothorax. It occurs due to a congenital defect of the lymphatic vessels but it may be associated with inflammation of the lymphatics, so-called lipogranulomatous lympangitis. The relationship with lipogranulomatous lymphangitis is currently unclear and it is possible that either condition could result in the development of the other. Secondary lymphangiectasia occurs with any pathological process that causes lymphatic obstruction, of which the most common are:

• Inflammation and subsequent fibrosis of the lymphatics, obstructing the lumina of the vessels.
• Neoplastic infiltration or erosion of the walls of lymphatic vessels.
• Obstruction of the thoracic duct, the major lymphatic vessel that runs through the chest. This may occur due to rupture and subsequent inflammation or due to the presence of a neoplastic mass.
• Right-sided heat failure (including cardiac tamponade) causes an increase in central venous pressure, reducing the pressure gradient between the thoracic duct and the subclavian veins with which it anastomoses.

• caval obstruction?
• hepatic disease?

Signalment

The disease is relatively common in dogs but rare in cats. Yorkshire terriers, Rottweilers and Norwegian Lundehunds are predisposed to the development of disease.

Diagnosis

Clinical Signs

Clinical signs are related to the loss of lymph and the resultant protein-losing enteropathy and fat malabsorption. The following signs are therefore common:

• Weight loss in the face of polyphagia due to loss of fat and protein.
• Chronic diarrhoea or steatorrhoea, the latter occurring due to the high fat content of the faeces. The presence of large quantities of fat in the intestinal lumen provides a substrate for bacteria which produce hydroxy-fatty acids as by-products. Bacterial proliferation may result in concurrent small intestinal bacterial overgrowth (SIBO) and the hydroxy-fatty acids act as potent secretagogues in the colon, leading to the production of diarrhoeic faeces.
• Effusions may develop for a number of reasons in animals with lymphangiectasia. Ascites composed of a transudate may develop in severely hypoproteinaemic animals but, in animals that develop secondary lymphangiectasia due to right-sided heart failure, a modified transudate may form due to portal hypertension. If the major lymphatic vessels of the abdomen are disrupted (by a neoplastic mass), chylous ascites may develop, although this is very rare. In animals with congenital lymphangiectasia or in those with disruption of the thoracic duct, chylothorax may also be described.
• Vomiting, lethargy and anorexia are not common clinical signs.

Laboratory Tests

The following parameters may be altered on haematological or biochemical analysis of blood samples:

Haematology

• Lymphopaenia occurs as lymphocytes are the major type of cell present in lymph and they are therefore lost into the intestinal lumen in large numbers.
• If an inflammatory process has developed (such as lipgranulomatous lymphangitis), there may be a monocytosis or neutrophilia.

Biochemistry

• Panhypoproteinaemia occurs in most forms of protein-losing enteropathy and refers to the loss of both plasma albumin and globulin.
• Hypocholesterolaemia and a reduction in the circulating concentration of triglycerides occur as these nutrients are lost into the intestinal lumen.
• Hypocalcaemia occurs due to hypoproteinaemia (reducing the total but not ionised calcium concentration) and due to vitamin D and calcium malabsorption. Hypocalcaemic tetany may be observed in animals which are severely hypocalcaemic and which then become stressed or excited.
• Hypomagnesaemia may also develop due to malabsorption but this is rarely recognised in clinical practice.
• Changes associated with SIBO are discussed here.

Lymphangiectasia Endoscopy- Copyright Karin Allenspach's lecture RVC

Other Tests

Further tests may be used to confirm the presence of protein-losing enteropathy, including measurement of faecal alpha-1 protease inhibitor concentration and faecal 51-Chromium albumin concentration after intra-venous injection.

Diagnostic Imaging

Ultrasonography

Ultrasound scans may reveal the presence of effusions (pleural fluid or ascites) and may be used to rule out other causes of PLE. The mucosa of affected intestinal loops may appear to be thickened and may also appear to have 'tiger stripes', although the latter finding is an unreliable indicator of lymphangiectasia.

Endoscopy

Grossly, multiple white lipid droplets with prominent mucosal blebs can be seen.

Histopathology

Preferably, a full thickness biopsy is needed for a definitive diagnosis.

Refer to Lymphangiectasia for pathology

It is essential to distinguish a true lymphangiectasia from a secondary lacteal dilation due to Inflammatory Bowel Disease (IBD). In the case of IBD, inflammatory infiltrate will be seen in the lamina propria, but the degree of infiltration may be underestimated if oedema is present.

Treatment

• Identify and treat the underlying cause if it is a secondary lymphangiectasia

Dietary modification

• Fat-restricted diet
• The diet needs to be calorific and highly digestible
• Supplementation of fat soluble vitamins
• Anecdotal report of glutamine supplementation

Immunosuppressive

• Prednisolone
• Anti-inflammatory and immunosuppressive effect may be beneficial.
• This is particularly true if there is associated lymphangitis, lipogranulomas or a lymphocytic-plasmacytic infiltration of the lamina propria.
• Azathioprine or Ciclosporin can also be considered

Antimicrobials

• Metronidazole or tylosin can be given
• This may be beneficial due to their potential immunomodulatory effect and modulation of the enteric flora
• Diuretics such as frusemide and spironolactone are used to manage effusions.

Fluid therapy

• Short term treatment with plasma or colloids can be given for plasma expansion.

Prognosis

Guarded. The response to treatment is generally poor although some dogs may do well. Dogs may be in remission for several years but the disease eventually progress to fulminant hypoproteinaemia.

From pathology

Pathology

Gross

• Small and large intestines may be affected.
• Dilation of lacteals.
• Oedema of intestinal mucosa.
• Distension of mesenteric lymphatics and lymph nodes.

Histological

• Accumulation of lipid-laden macrophages and granulomatous response around distended lymphatics.

References

• Ettinger, S.J. and Feldman, E. C. (2000) Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2 (Fifth Edition) W.B. Saunders Company.
• Hall, E.J, Simpson, J.W. and Williams, D.A. (2005) BSAVA Manual of Canine and Feline Gastroenterology (2nd Edition) BSAVA
• Nelson, R.W. and Couto, C.G. (2009) Small Animal Internal Medicine (Fourth Edition) Mosby Elsevier.