Bone Marrow 2 Flashcards
How does the thymus develop as an animal ages?
The thymus is at its maximal mass at birth and regresses (involutes) with age
Why is the thymus considered a “composite” organ?
Because it contains both lymphoid and epithelial tissues
What does the lymphoid component of the thymus do?
It matures T-cells (few T-cells survive this process since the thymus is picky)
What does the epithelial component of the thymus do?
It supports the development of T-cells
What two diseases can a deficiency of the thymus result in?
Immunodeficiency or autoimmunity
What are the disorders of a “too-small” thymus (three)?
- Severe Combined Immunodeficiency Disorder (SCID) (lymphocytes never populated the thymus to begin with)
- Involution (increased loss)
- Lymphoid atrophy (increased loss)
What are the disorders of a “too-large” thymus?
Neoplasia (thymoma or lymphoma)
What is Severe Combined Immunodeficiency Disorder (SCID)?
A genetic defect in the common lymphoid stem cell line leading to defective cell-mediated and humoral immune responses
(I think basically this is where you don’t make functional T-cells and B-cells, therefore your adaptive immune response is garbage)
Which animals can get SCID?
Dogs, mice, humans, and horses
What horse breeds commonly get SCID?
Arabian horses
What are the classic necropsy findings in SCID?
Bronchopneumonia in combination with an extremely small thymus, lymph nodes, and spleen
What does thymic atrophy result in?
An acquired immunodeficiency
Which viruses can cause thymic atrophy in dogs, cats, cows, and horses?
Dogs: Parvovirus and distemper virus
Cats: Panleukopenia virus
Cows: BVDV
Horses: EHV-1 in aborted foals
Thymic atrophy in puppies and kittens should steer you towards parvovirus or panleukopenia
What are four non-viral causes of thymic atrophy?
- Malnutrition*
- Toxins
- Chemotherapeutic agents
- Stress
What are the main differences between thymic lymphoma and thymomas?
Thymic lymphoma
- Tumour composed of malignant T-cells
- Aggressive, seen in younger animals
- More often seen in cats and cows (cows is associated with sporadic form, not BLV. In cats it’s more FeLV associated)
Thymoma
- Tumour derived from the epithelial components
- Uncommon
- Occurs in older animals
- Usually benign
- Can cause autoimmune diseases (ex. myasthenia gravis)
How can you differentiate between thymic lymphomas and thymomas grossly?
Trick question - you can’t really tell from gross examination. You need to use the signalment, clinical signs, and histopathology to differentiate
If you are suspicious of a lymph node pathology, what should you check first?
You should always trace it back to the site of lymph drainage
What are the disorders of a “too-small” lymph node (five)?
- SCID
- Aging
- Lack of antigenic stimulus
- Viral (BVD, CDV)
- Cachexia and malnutrition
What is the term for a large lymph node?
Lymphadenopathy or lymphadenomegaly
What are the disorders of a “too-large” lymph node (five)?
- Reactive lymphoid hyperplasia (ex. bacterial bronchopneumonia)
- Acute lymphadenitis (ex. strangles)
- Chronic lymphadenitis
- Primary neoplasia (ex. lymphoma)
- Metastatic neoplasia (ex. metastatic melanoma)
How can you tell the difference between reactive lymphoid hyperplasia and neoplasia?
With reactive lymphoid hyperplasia you should still see a distinct cortex and medulla. In neoplasia, you usually lose all distinguishing characteristics
What are the disorders of a “too-small” spleen?
Blood related:
- Contraction from excitement or shock
Lymphocyte related:
- Cachexia
- Aging
- Splenic lymphoid hypoplasia (due to SCID)
What are the disorders of a “too-large” spleen (four)?
- Bloody spleen (uniform splenomegaly with blood)
- Meaty spleen (uniform splenomegaly without blood)
- Splenic nodules with bloody consistency
- Splenic nodules with firm consistency
Name three differentials for uniform splenomegaly with blood
- Congestion (due to torsion or barbiturate administration)
- Acute hemolytic anemia
- Acute hyperemia (caused by acute septicemia, ex. anthrax)
What does uniform splenomegaly with blood look like grossly?
These spleens are big, dark red to blue-black, and ooze blood on section
