Lymphoid System Pathology III (continued)

What causes Enzootic Bovine Leukosis

cell-associated retrovirus – Bovine Leukosis Virus (BLV) - Retrovirus

How is Enzootic Bovine Leukosis spread

horizontal, via blood (infected lymphocytes)

– Once infected, an animal is infected for life

What is Seroprevalence:

many cattle are infected, but FEW develop disease

Only <5% of seropositive animals develop what

tumors (adults)

~66% of U.S. dairy herds are what

seropositive, and 13–48% of individual dairy cattle

What do we mean by

PL may be evident for years, usually without tumor development (otherwise asymptomatic)sistent lymphocytosis (PL)

What is the % of Persistent lymphocytosis (PL) of cows that get it

~30% of seropositive cattle develop PL

What is the most common outcome of BLV infection

Persistent lymphocytosis (PL)

How can we determine the clinical signs for Lymphoma (<5%)

Clinical signs depend on the location of the tumor or tumors

How many sites are there for Lymphoma (<5%)

4–5 characteristic sites

Where do the tumors of BLV occur in and which is most common

• Lymph nodes (most common) – retrobulbar: proptosis; pharyngeal: dysphagia; mesenteric: palpable masses

• Abomasum – obstruction, ulceration

• Heart – heart failure

• Uterus – infertility, palpable masses

• Spinal cord – posterior paresis

Which Sporadic Bovine Lymphoma are Not BLV-associated; less common

• Calf type – birth to 6 months old

– Generalized lymphadenopathy, leukemia; terminal disease

• Juvenile type (thymic lymphoma) – yearling cattle

– Thymus from neck to base of heart; massive thymic enlargement – dyspnea, bloat, choke, swollen neck, brisket edema

• Cutaneous – young adults

– Plaque-like, round, raised skin lesions that may wax and wane over months

– Ultimately (12–18 mo.) develop deep organ involvement

Equine Lymphoma is less common in what animal

• Less common than in dogs, cats and cattle

What May be the most common disseminated neoplasm of horses

Equine Lymphoma

What is the common presentation for Equine Lymphoma

lymphadenomegaly and/or massive splenomegaly

What is the common complaint when a horse is affected by Equine Lymphoma

Weight loss is a common complaint

What does red mean in the LN

• Draining hemorrhage

• Lymphadenitis

• Hemal node

What animal commnly gets Hemal node – when the LN is red

– Occur in ruminants

– Similar structure to lymph node but filled with blood

– Unknown function

The LN is black/brown what causes and what disease is associated with

• Likely hemosiderin (erythrocyte breakdown)

• Less likely carbon (anthracosis) – if pulmonary lymph nodes

• Metastatic melanoma

What is the defintion of Lymphedema

edema accumulation due to decreased lymph drainage

What is the primary causes of Lymphedema

• Congenital abnormalities in lymphatics or easy flow through lymph node

– Draft horses – progressive lymphedema

What is the secondary causes of Lymphedema

• Lymphangitis

• Regional fibrosis/obesity

• Tumors

• Burns

• Compression

What is the definition for Lymphangiectasia

Dilation of normally formed lymphatics secondary to obstruction

What are the primary causes for Lymphangiectasia

• Intestinal lymphangiectasia leads to protein-losing enteropathy

• Ruptures of dilated lacteals leads to protein loss and can induce granulomatous inflammation

• Chronic diarrhea, weight loss, hypoalbuminemia, hypocholesterolemia, and lymphopenia, with ascites, pleural effusion, or peripheral edema when protein loss is severe

What animal is affected by Lymphangectasia

• Congenital in dog breeds (Yorkshire Terrier, etc.)

What causes Chylothorax

– Leakage or rupture of thoracic duct

– Secondary to obstruction

• Neoplasia, right heart failure, etc

Who commonly gets Chylothorax

Most common in cats

What is Lymphangitis and examples of dx

• Granulomatous lymphangitis occurs with Johne’s disease

• Sporadic lymphangitis (horses; unknown cause)

• Ulcerative lymphangitis (horses; Corynebacterium pseudotuberculosis)

What is Lymphangiosarcoma

malignant neoplasm of endothelial cells of the lymphatic system

Which animal rarely gets Neoplasia

• Rare – dog and cat subcutis most frequently – Cats – ventral abdomen

Neoplasia Difficult to distinguish from

hemangiosarcoma

What kind animal (age) has red marrow

(newborns, very young)

What kind animal (age) has yellow marrow

(adult)

How do we obtain bone marrow and what test do we use

• Cytology – best for individual cell, cellular differentiation, and cell detail

• Biopsy – best for cellularity, tissue architecture

• Diagnosis of fibrosis, necrosis, infiltrative disease

What is Hyperplasia

increase in cell numbers

What is Hypoplasia

decreased in cell number

What is Aplasia

absence of hematopoietic tissue

What is Dysplasia

alteration of shape, size, or organization of cells (may progress to neoplasia)

What is Leukemia

–Neoplasms of hematopoietic cells that originate in the bone/have neoplastic cells in circulation

What do we call when the bone marrow is inflammed

myelitis

What causes myelitis

– Infectious agents reach the marrow hematogenously or directly by trauma

– Usually accompanied by bone involvement (osteomyelitis)

MALT includes:

– BALT (bronchus-associated

– GALT (gut-associated)

– Tonsils

– Lymphoid nodules in the nasal cavity, pharynx, conjunctive, and urinary bladder

Why does atrophy occur in Mucosa-Associated Lymphoid Tissue

– Lack of antigenic stimulus

– Malnutrition

– Cachexia

– Aging

Necrosis – often associated with what

viral infections

What are the structures and components for Thymus

– Primary lymphoid organ (together with bursa of fabricius and bone marrow)

– Multilobed organ divided by fibrous septae

– Composite organ (epithelial and lymphoid cells)

– No lymphoid follicles nor B-lymphocytes

• Cortex – T-lymphocytes

• Medulla – Epithelial cells (Hassall’s corpuscles), dendritic cells

What is the function for thymus

– Development of T-lymphocytes that arrive as precursors from the bone marrow

– T lymphocyte selection → self tolerance

– >95% of T cells that enter thymus are destroyed

What causes Involution (atrophy)

Normal aging process

What causes Lympholysis (lymphocyte necrosis)

– Many causes (viruses, malnutrition, toxins, ionizing radiation, infections)

– Must be differentiated from normal involution

What is Severe Combined Immunodeficiency (SCID)

– Both humoral and cell-mediated immunity are deficient

– Affected foals succumb to infection at an early age

– Lymphoid tissues are smaller than normal

– Depletion of lymphocytes

What animals are affected from Thymic Hypoplasia

Arabian foals; Jack Russel Terrier Bassett hound, Welsh Corgi

Thymitis occurs when ?

Occurs with equine herpesvirus 1 abortions and postweaning multisystemic wasting syndrome (PMWS) of pigs

PMWS results in

granulomatous thymitis and intracytoplasmic inclusion bodies

Lesions of EHV-1 include

lymphocytes necrosis and intranuclear viral inclusions

What are Thymic cysts and where do we find them?

– Remnants of branchial arch epithelium

– Incidental findings

What are the clinical signs for Thymus – Increased Thymic Size

• Clinical signs develop from progressively increased size of the thymus and its effects on adjacent structures

– Respiratory tract

• Dyspnea, cough

– Digestive tract

• Regurgitation

– Cranial vena cava

• Edema, swollen head and neck

– Thoracic duct

• Chylothorax (pleural effusion)

What animals are affected by Thymic (mediastinal) lymphoma

– Adult dogs (– Most common mediastinal tumor in older dogs)

– Cats – bimodal age distribution (young or older)

• Average age in cats = 2–3 years (10–20% are FeLV+)

• Cats – typically no involvement of other organs, except bone marrow

Thymus – Thymic Lymphoma causes what

– Often causes a pleural effusion

– Tends to be aggressive, invasive, and characterized by neoplastic lymphocytes in the pleural cavity

What is Thymoma

– Tumor of epithelial component of the thymus

– BUT, tumor may be mostly epithelial cells, mostly mature (non-neoplastic) lymphocytes, or a mix

Which animal can get Thymoma

Uncommon in all species except goats

In Thymoma what else is also uncommon

Metastasis and invasion are uncommon

Paraneoplastic syndromes are common in what kind of animals

small animals

Is Paraneoplastic syndromes an –Acquired autoimmune disorder?

• Especially myasthenia gravis and polymyositis

–Acquired autoimmune disorders

Why is megaesophagus common?

• Poor neuromuscular conduction with myasthenia gravis and weakness of muscle with polymyositis