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THIS MONTH 
More about Platelets 2 - Thrombopathias
NWL Joins Dechra Pharmaceuticals PLC
Next Clin Path Club meeting
Clin Path Club Dates for 2001
NWL Wins Major Contract
New Courier Service
Diagnosis of Peripheral Lymphadenopathy in the Dog
Tail End: "Black Cats Really are Unlucky"

More About Platelets 2 - Thrombopathias
“Thrombopathias may be inherited or acquired.’’

• By definition, patients suffering from thrombocytopathias have prolonged bleeding times, adequate platelet numbers, and normal coagulation profiles and are not suffering from von Willebrand’s disease. 

Thrombopathias may be inherited or acquired
Inherited thrombopathias
Several inherited defects have been identified, the mechanisms are complex and in some cases not fully understood. One example is Glanzmann’s thrombasthesia. In very basic terms there appears to be a reduction in the amount of the membrane glycoprotein GPIIb-IIIa. This protein, the `fibrinogen receptor’, is exposed during activation and shape change, and enables the cross linking of platelets via fibrinogen bridges, resulting in aggregation. Thus, lack of GPIIb-IIIa prevents normal aggregation. This condition has been identified in Otterhounds and Great Pyrenees. Other inherited thrombopathias are seen in Bassett Hounds, American Cocker Spaniels and Spitz dogs.
Acquired Thrombopathias
Acquired functional defects arise for a variety of reasons, including immune-mediated disease, iatrogenic causes, DIC, neoplasia and organ failure. These conditions are also cited as causes of thrombocytopenia and it may be a combination of thrombocytopenia and thrombopathia working simultaneously to produce the bleeding disorder.

Immune-mediated diseases
These have been discussed already. Antibodies directed against various platelet antigens often block essential receptor sites such as GPIIb-IIIa and interfere with aggregation. This is usually accompanied by premature removal of the platelet antigen-antibody complex from the circulation.

Iatrogenic causes
Many drugs are known or suspected to interfere with platelet function. In the case of aspirin, this has been exploited for many years in the prevention of thromboembolic disease. Aspirin effectively blocks the arachidonic acid pathway,( a step in the basic platelet reaction), by irreversibly inhibiting the enzyme cyclo-oxygenase and prevents formation of thromboxane A. Thromboxane A is central to amplification of the basic platelet reaction via the recruitment and activation of additional platelets. As the inhibition is irreversible, this effect persists throughout the platelets entire lifetime of 5-7 days even following drug withdrawal.
Other non-steroidal anti-inflammatory drugs have a similar mode of action but their interactions with cyclo-oxygenase are reversible, therefore function is inhibited only during therapy.
Many other drugs may affect platelet function including calcium channel blockers, barbiturates, beta-blockers, antibiotics, oestrogens and chondroitin sulphate. The range is wide and this highlights the importance of accurate history taking, if a patient is receiving any medication, it should probably be viewed with suspicion - rather a case of guilty until proven innocent!

DIC
Generalised activation of the clotting cascade with systemic production of fibrin and thrombus formation results in depletion of clotting factors and thrombocytopenia due to platelet consumption. Subsequently fibrinolysis occurs with the formation of fibrin degradation products which coat the platelet membrane, block the fibrinogen receptor sites and interfere with aggregation. 

Organ failure
Uraemia associated with renal disease restricts adhesion of platelet membrane proteins to damaged endothelial surfaces, thereby disrupting platelet function at a very early stage. The extent of the problem is directly proportional to the degree of azotaemia, and is not influenced by the amount or composition of Von Willebrand factor. Severe liver disease will compromise both primary and secondary haemostasis in a variety of ways, including the decreased production of fibrinogen; that prevents inter-platelet cross-linking, reduced production of other clotting factors and the likely involvement of DIC.

To summarise
Thrombocytopenias and thrombopathias can result from a seemingly colossal range of conditions, medications and situations. They can occur simultaneously and distinguish between quantitive and qualitative abnormalities and may become academic. 
Thorough history taking, a knowledge of normal haemostasis and using appropriate laboratory tests should help to pinpoint the problem and direct the clinician towards appropriate therapy. Haemostasis is a fascinating subject, and definitely an area in which it is essential to know what is right before trying to establish what is going wrong!

Sue Beck BVMS MRCVS

This is the concluding part of a 4 part series. See the newsletter archive for previous parts. 
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NWL Joins Dechra Pharmaceuticals

NWL recently became part of Dechra Pharmaceuticals PLC. You may already be aware that other companies in the Dechra group include; National Veterinary Services PLC (NVS) the largest UK veterinary wholesaler; Arnolds Veterinary Products Ltd, supplier of equipment and speciality pharmaceuticals and Dales Pharmaceuticals Ltd, a contract pharmaceuticals manufacturer and packer. Last year the Dechra group turned over £156.4 million.

We have chosen a business association with Dechra because we believe they can provide the resources we need to continue to grow the business. Over the past 3 years NWL has expanded at over 25 % per annum. This association will enable us to continue to expand our facilities and strengthen the professional and management teams. 

The laboratory will continue to be jointly operated by Tom Williams and Alistair Parker.

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CLIN PATH CLUB 
The Clin Path Club meetings are open to all veterinary surgeons and veterinary nurses.

Next Meeting: Thursday 11th July 2002 

Venue: Swallow Hotel, Samlesbury, Preston New Road, Preston. (Leave M6 J31, follow A59 signs to Blackburn, hotel just before 1st traffic lights)

Speaker: Jane Miller BVetMed FRCPath MRCVS: Canine Anaemia: A practical approach to haematology in Practice.

Case book studies: If you would like to present an interesting case please contact Jane Miller on 01253 899215 or e-mail

To book your place, request further information or a location map call Joanne Kenyon on 01253 899215 or e-mail

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CLIN PATH CLUB - Dates for 2002 
Please make a note in your diary of the forthcoming meetings :- 

• Thurs 12th September 2002 Dr Ian Ramsey BVSc PhD Dip ECVIM MRCVS: Recent advances in the diagnosis and treatment of Canine hyperadrenocorticism
• Thurs 14th November 2002 Dr A Coughlan BVSc Cert VA DSAS (Orth) PhD FRCVS Working up the lame dog "Tricks and Traps"

Quote “An excellent way to top up your CPD"

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NWL WINS MAJOR CONTRACT
Contract was won against stiff opposition 

NWL have won a major contract with the Meat and Livestock Commission (MLC) to monitor the national pig herd for Salmonella. The contract was won against stiff opposition from 16 other laboratories.
Joint Managing Director Alistair Parker said “One of the critical factors in winning the contact was being a UKAS accredited Laboratory”.

The Testing programme starts in June and involves the testing of over 3000 pig muscle juice samples a week from over 20 participating abattoirs for at least 3 years.
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NEW COURIER SERVICE
NWL clients who are also National Veterinary Services NVS customers will be able to take advantage of a new sample collection service to be launched by NVS on 10th June 2002.

This service is available Monday to Thursday and will provide practices with a convenient alternative option to the postal service. When your normal NVS delivery arrives, hand the NWL samples to the van driver who will transport them in a secure, insulated container for guaranteed next day delivery to NWL. Where appropriate results will be reported to the practice by fax before 6.30pm the same day.

This service is at present open to NWL/NVS customers only who have a daily delivery from NVS.
NVS customers, who don't have a daily delivery, but wish to use the courier service on a daily basis, should contact their NVS Territory Manager who will be able to provide you with an appropriate solution for the collection of samples.

NWL clients who don't use NVS as a wholesaler and who are interested in the courier service, please contact NWL Client Services Co-ordinator, Joanne Kenyon to discuss.

NB The new service will not effect those clients already receiving an NWL, same day or overnight courier collection.
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Diagnosis of Peripheral Lymphadenopathies in the Dog
“Sampling should be done before any therapy, particularly if lymphoma is suspected”

Lymphadenopathy is relatively common and may affect one or more lymph nodes. The three most common causes of lymphadenopathy are neoplasia (lymphoma or metastasis), hyperplasia and lymphadenitis. For diagnosis, cytology and histopathology are the techniques of choice. Sampling should be done before any therapy is administered, particularly if lymphoma is suspected. Corticosteroids make lymphoma cells appear morphologically more mature. 

Sampling
Diagnostic cytology needs fine needle aspirate (FNA) smears from one or more affected lymph nodes. To avoid disruption of fragile cells it is important to use using minimal suction on the biopsy syringe. Lymphoma cells particularly can be easily damaged. Release suction before the needle is withdrawn from the node. Aspirated material should not appear in the syringe hub. Express the aspirate on one or preferably more slides. Place a drop of sample towards one end, spread with another slide in the same way as making a blood smear. Important: thoroughly air dry the smears, do not use a coverslip. Label all slides with the owners and animals names and the aspirate site. Send the dried slides in a slide mailer to the laboratory for staining and interpretation. A leaflet on how to take FNA’s is available on request.

FNA’s
Diagnosis of lymphadenitis, reactive hyperplasia and neoplasia can all be made from good FNAs. Poor cell yield or aspirate quality and or smear preparation will almost certainly result in a non-diagnostic sample. It should be remembered that some lymphomas, particularly the rarer follicular type are difficult to identify by FNA and may need a formalin fixed biopsy for diagnosis. 

Histopathology
If the opportunity to take a full lymph node biopsy presents its self, this is the most reliable diagnostic approach. A formalin fixed biopsy provides  the opportunity to examine the tissue architecture and a larger portion of the node. This is useful for diagnosis of some of the less common types of lymphoma and when a lymph node is only partially infiltrated by neoplastic cells. Formalin fixed tissue can also be used for immunophenotyping lymphomas. An important aid to staging lymphomas.

Precautions
Sterile fresh biopsy material for culture as well formalin fixed biopsy should be submitted if a lymphadenitis is suspected. Again this should be taken before antibiotic therapy is started. 
It is important to keep formalin fixed tissue well away from smears and samples for microbiology.

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Tail End 
“Black Cats really are unlucky”

BLACK cats can bring bad luck if their owners suffer from allergies, according to a recent survey.
Black or dark-coloured cats cause more severe reactions in their owners than light-coloured ones, according to the study in Long Island College Hospital, New York. Researchers polled 320 owners at an allergy clinic and found dark cats were two to four times more likely to cause moderate or severe allergic reactions, such as sneezing and itchy eyes, than lighter coloured ones.

It has been suggested that black cats might produce more of a potent allergen called Fel d1. "On the other hand, they might have some other unknown antigen."

"Cat dander, similar to human dandruff, was once thought to be the main cause of allergies. But it is the Fel d1 substance, produced in the sebaceous glands of the skin and saliva, that is the major culprit."

Further reading about black cats and bad luck. http://www.liii.com/~nyask/cat-report2.html
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