Pathology of the LHS

Question 1

Name the primary lymphoid organs

Answer 1

BM and thymus

Question 2

Name secondary lymphoid organs

Answer 2

LNs, spleen and MALT

Question 3

What is the origin of most pathology of the lymphoreticular system?

Answer 3

infection, immune-mediated disease, neoplasia

Question 4

Name 3 thymic diseases

Answer 4

• thymic hypoplasia
• thymic lymphoma (cats)
• thymoma (dogs)

Question 5

Outline thymic hypoplasia

Answer 5

• congenital/developmental (often associated with primary immunodeficiency e.g. X-linked SCID)
• systemic viral lymphoid depleton (FeLV, FIV, CDV)

Question 6

Outline feline thymic lymphoma

Answer 6

• association with FeLV infection

- it is of immature TCs

Question 7

CS - thymic lymphoma

Answer 7

• dyspnoea*
• anorexia
• wt loss

Question 8

Dx - thymic lymphoma

Answer 8

• thoracic radiography (mass in anterior thorax, effusion)

- cytology of pleural fluid / FNAB

Question 9

Tx - thymic lymphoma

Answer 9

Chemotherapy

Question 10

Outline canine thymoma

Answer 10

• neoplasia of thymic epithelial cells

- GSDs and labrador retrievers

Question 11

CS - canine thymoma

Answer 11

• dyspnoea
• dysphagia
• thoracic effusion

Question 12

Dx - canine thymoma

Answer 12

• thoracic radiography
• ultrasound
• cytology of fluid / FNAB

Question 13

Tx - canine thymoma

Answer 13

sugical excision +/- chemotherapy

Question 14

Px - canine thymoma

Answer 14

Good if tumour has not spread beyond thymic capsule (i.e. stage 1 without paraneoplastic disease)

Question 15

What is canine thymoma associated with?

Answer 15

paraneoplastic syndromes (myasthenia gravis/ hypercalcaemia of malignancy)

Question 16

How do lymphocytes enter LNs?

Answer 16

Via High Endothelial Venules (HEVs)

Question 17

How do lymphocytes return to blood if they don’t recognise an antigen?

Answer 17

via the efferent lymphatic vessels and thoracic duct

Question 18

T/F: antigen presenting cells (APCs) migrate into the LNs from teh tissues and present Ag to incoming TCs

Answer 18

True (so LNs trap foreign material and optimise exposure of lymphocytes to Ag)

Question 19

Origin of effector TCs and Ab

Answer 19

both from plasma cells

Question 20

What happens to thoracic duct in chylothorax?

Answer 20

it is damaged, perforated or eroded (often by a tumour) and the ‘efferent’ lymph leaks out into thoracic cavity

Question 21

CS - chylothorax

Answer 21

• compromised respiratory function

- disrupted migratory pathway of lymphocytes leading to a lymphopaenia

Question 22

What happens when malignant cells attempt to metastasise via lymphatics?

Answer 22

the can become trapped in drainage LNs, establishing secondary sites of tumour formation: e.g. tonsillar SCC, MCT and malignant melanoma

Question 23

Define lymphadenopathy

Answer 23

LN enlargement

Question 24

What should you determine when lymphadenopathy has been identified?

Answer 24

if:

• localised (regional disease)
• generalised (systemic disease - is spleen enlarged too?)

Question 25

2 most common causes of enlarged LNs

Answer 25

- infection | - neop;asia

Question 26

Diagnosis of generalised lymphadenopathy

Answer 26

``` HAEMATOLOGY: - lymphopaenia suggests viral infxn - neutrophilia with left shift suggests bacterial infxn - eosinophilia suggests parasitic infection or allergy LYMPH NODE BIOPSY: - FNAB - Core biopsy (TruCut) - Excisional biopsy ```

Question 27

Ddx - generalised lymphadenopathy

Answer 27

- Reactive LN - lymphadenitis - primary neoplasia (lymphoma) - secondary neoplasia (metastasis)

Question 28

Describe reactive LN histopathology

Answer 28

normal architecture with increased cellularity. secondary follicles with germinal centres.

Question 29

Describe lymphadenitis histopathology

Answer 29

active infection within the LN itsel. Similar to reactive LN except areas of pyogranulomatous inflammation often present. Can be subdivided into suppurative, caseous or granulomatous.

Question 30

Describe primary neoplasia histopathology

Answer 30

usually complete lack of normal architecture. Large numbers of abnormal lymphocytes present.

Question 31

Describe secondary neoplasia (metastasis) histopathology

Answer 31

areas of normal lymphoid tissue infiltrated by neoplastic cells (focal or diffuse)

Question 32

Cause of strangles

Answer 32

Streptococcus equi

Question 33

Cause of caseous lymphadenitis (sheep, goats)

Answer 33

Corynebacterium pseudotuberculosis

Question 34

Cause of granulomatous lymphadenitis

Answer 34

Mycobacterium (TB/ Johne's), many macrophages in these lesions

Question 35

T/F: mast cells are not usually found in LN

Answer 35

True

Question 36

List types of spleen pathology

Answer 36

- trauma/ rupture/ haematoma (e.g. RTA) - torsion - infarcation (Classical Swine Fever)

Question 37

What to determine with spleen pathology

Answer 37

Diffuse or nodular?

Question 38

Ddx - diffuse splenomegaly

Answer 38

- Venous congestion - Lymphoid hyperplasia - Systemic amyloidosis - Neoplasia (lymphoma, myeloma)

Question 39

Causes of venous congestion causing diffuse splenomegaly

Answer 39

- following torsion | - post-mortem artefact following barbiturate administration

Question 40

Cause of lymphoid hyperplasia causing diffuse splenomegaly

Answer 40

systemic infectious/ inflammatory/ I-M disease

Question 41

Ddx - nodular splenomegaly

Answer 41

- nodular hyperplasia (incidental in older animals) - abscess / cyst (infectious agent) - primary neoplasia (lymphoma, haemangioma, HSA) - metastatic disease (e.g. MCT)

Question 42

Which viruses particularly impact on the lymphoreticular system?

Answer 42

- Malignant Catarrhal fever (a herpes virus) - Classical Swine Fever - FeLV/ FIV/ Canine distemper virus - EIA

Question 43

Describe classical swine fever (CSF)

Answer 43

- notifiable - CS: pyrexia, diarrhoea, petechial haemorrhages (classically splenic infarcts), neuro signs - CAUSE: last in Norfolk 2000 d/t imported infected meat

Question 44

Which bacteria particularly impact on the lymphoreticular system?

Answer 44

- Bacillus anthracis (Anthrax) - Streptococcus equi (Strangles, suppurative lymphadenitis) - Corynebacterium pseudotuberculosis (caseous lymphadenitis) - Mycobacterium boviis (TB) / M. avium paratuberculosis (Johne's, granulomatous lymphadenitis)

Question 45

Name 4 protozoa which particularly impact on the lymphoreticular system

Answer 45

- leishmaniosis - babesiosis - ehrlichiosis - theileriosis

Question 46

Describe Bacillus anthracis (anthrax)

Answer 46

- DON'T PME but notify the APHA - UK notifiable - ruminant sudden death with haemorrhage from orifices, splenomegaly - pigs/ horses have a more protracted illness