Pathology of the LHS Flashcards
Name the primary lymphoid organs
BM and thymus
Name secondary lymphoid organs
LNs, spleen and MALT
What is the origin of most pathology of the lymphoreticular system?
infection, immune-mediated disease, neoplasia
Name 3 thymic diseases
- thymic hypoplasia
- thymic lymphoma (cats)
- thymoma (dogs)
Outline thymic hypoplasia
- congenital/developmental (often associated with primary immunodeficiency e.g. X-linked SCID)
- systemic viral lymphoid depleton (FeLV, FIV, CDV)
Outline feline thymic lymphoma
- association with FeLV infection
- it is of immature TCs
CS - thymic lymphoma
- dyspnoea*
- anorexia
- wt loss
Dx - thymic lymphoma
- thoracic radiography (mass in anterior thorax, effusion)
- cytology of pleural fluid / FNAB
Tx - thymic lymphoma
Chemotherapy
Outline canine thymoma
- neoplasia of thymic epithelial cells
- GSDs and labrador retrievers
CS - canine thymoma
- dyspnoea
- dysphagia
- thoracic effusion
Dx - canine thymoma
- thoracic radiography
- ultrasound
- cytology of fluid / FNAB
Tx - canine thymoma
sugical excision +/- chemotherapy
Px - canine thymoma
Good if tumour has not spread beyond thymic capsule (i.e. stage 1 without paraneoplastic disease)
What is canine thymoma associated with?
paraneoplastic syndromes (myasthenia gravis/ hypercalcaemia of malignancy)
How do lymphocytes enter LNs?
Via High Endothelial Venules (HEVs)
How do lymphocytes return to blood if they don’t recognise an antigen?
via the efferent lymphatic vessels and thoracic duct
T/F: antigen presenting cells (APCs) migrate into the LNs from teh tissues and present Ag to incoming TCs
True (so LNs trap foreign material and optimise exposure of lymphocytes to Ag)
Origin of effector TCs and Ab
both from plasma cells
What happens to thoracic duct in chylothorax?
it is damaged, perforated or eroded (often by a tumour) and the ‘efferent’ lymph leaks out into thoracic cavity
CS - chylothorax
- compromised respiratory function
- disrupted migratory pathway of lymphocytes leading to a lymphopaenia
What happens when malignant cells attempt to metastasise via lymphatics?
the can become trapped in drainage LNs, establishing secondary sites of tumour formation: e.g. tonsillar SCC, MCT and malignant melanoma
Define lymphadenopathy
LN enlargement
What should you determine when lymphadenopathy has been identified?
if:
- localised (regional disease)
- generalised (systemic disease - is spleen enlarged too?)
2 most common causes of enlarged LNs
- infection
- neop;asia
Diagnosis of generalised lymphadenopathy
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
Ddx - generalised lymphadenopathy
- Reactive LN
- lymphadenitis
- primary neoplasia (lymphoma)
- secondary neoplasia (metastasis)
Describe reactive LN histopathology
normal architecture with increased cellularity. secondary follicles with germinal centres.
Describe lymphadenitis histopathology
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.
Describe primary neoplasia histopathology
usually complete lack of normal architecture. Large numbers of abnormal lymphocytes present.
Describe secondary neoplasia (metastasis) histopathology
areas of normal lymphoid tissue infiltrated by neoplastic cells (focal or diffuse)
Cause of strangles
Streptococcus equi
Cause of caseous lymphadenitis (sheep, goats)
Corynebacterium pseudotuberculosis
Cause of granulomatous lymphadenitis
Mycobacterium (TB/ Johne’s), many macrophages in these lesions
T/F: mast cells are not usually found in LN
True
List types of spleen pathology
- trauma/ rupture/ haematoma (e.g. RTA)
- torsion
- infarcation (Classical Swine Fever)
What to determine with spleen pathology
Diffuse or nodular?
Ddx - diffuse splenomegaly
- Venous congestion
- Lymphoid hyperplasia
- Systemic amyloidosis
- Neoplasia (lymphoma, myeloma)
Causes of venous congestion causing diffuse splenomegaly
- following torsion
- post-mortem artefact following barbiturate administration
Cause of lymphoid hyperplasia causing diffuse splenomegaly
systemic infectious/ inflammatory/ I-M disease
Ddx - nodular splenomegaly
- nodular hyperplasia (incidental in older animals)
- abscess / cyst (infectious agent)
- primary neoplasia (lymphoma, haemangioma, HSA)
- metastatic disease (e.g. MCT)
Which viruses particularly impact on the lymphoreticular system?
- Malignant Catarrhal fever (a herpes virus)
- Classical Swine Fever
- FeLV/ FIV/ Canine distemper virus
- EIA
Describe classical swine fever (CSF)
- notifiable
- CS: pyrexia, diarrhoea, petechial haemorrhages (classically splenic infarcts), neuro signs
- CAUSE: last in Norfolk 2000 d/t imported infected meat
Which bacteria particularly impact on the lymphoreticular system?
- Bacillus anthracis (Anthrax)
- Streptococcus equi (Strangles, suppurative lymphadenitis)
- Corynebacterium pseudotuberculosis (caseous lymphadenitis)
- Mycobacterium boviis (TB) / M. avium paratuberculosis (Johne’s, granulomatous lymphadenitis)
Name 4 protozoa which particularly impact on the lymphoreticular system
- leishmaniosis
- babesiosis
- ehrlichiosis
- theileriosis
Describe Bacillus anthracis (anthrax)
- DON’T PME but notify the APHA
- UK notifiable
- ruminant sudden death with haemorrhage from orifices, splenomegaly
- pigs/ horses have a more protracted illness
