Erythrocytosis and Polycythemia/Lymph Node Cytology

Question 1

describe erythrocytosis and polycythemia

Answer 1

erythrocytosis: increase in RBC mass (HCT/PCV, RBC count, and/or Hgb)

polycythemia: many cells in the blood
-most pathologists use this term only for neoplasia

Question 2

why is more blood bad?

Answer 2

1. increases blood viscosity, causing sludging of RBCs in vessels
2. leads to impaired blood flow:
   -decreased tissue oxygenation
   -congested mucous membranes
   -dilated retinal vessels
   -seizures

Question 3

describe breed specific differences in RBC mass

Answer 3

some breeds have a higher RBC mass in health

-sighthounds, greyhounds, some dachshunds

-racing horses, warm-blooded breeds

Question 4

describe erythropoietin

Answer 4

1. primary hormonal regulator of RBC production
2. produced by the fetal liver and the adult kidney
3. upregulated by renal hypoxia (NOT RBC mass)
   -anemia
   -poor renal perfusion
   -poor oxygenation of blood

Question 5

what are the 2 types of erythrocytosis?

Answer 5

1. relative:
   -NOT a true increase in RBC mass
   -2 big causes:
   –dehydration: decreased plasma volume (hemoconcentration); history, PE findings, increased protein, USG, asotemiz
   –splenic contraction: excitable animal (epi response), redistribution of RBCs from spleen, common in cats and horses
2. absolute: TRUE increase in RBC mass
   -primary: low/normal Epo, polycythemia vera
   -secondary: increased Epo
   –appropriate: hypoxia induced (high alt, lung disease, right to left cardiac shunts)
   –inappropriate: no systemic hypoxia (renal diseases, epo-secreting tumors, exogenous)

Question 6

describe dehydration causing relative erythrocytosis

Answer 6

1. most common cause of mild to moderate erythrocytosis
2. NOT an absolute increase in RBC mass, just a decrease in plasma volume
3. PE findings:
   -dry or tacky MM, skin tent

4, lab findings:
-increased proteins (TP and albumin)
-highly concentrated urine (high USG)
-possible pre-renal azotemia (increased urea and creatinine)

5. tx: rehydrate the patient and recheck

Question 7

describe splenic contraction causing relative erythrocytosis

Answer 7

1. no dehydration
2. NOT an increase in RBC mass; RBCs are redistributed into circulation from splenic contraction
3. transient and secondary to fear, excitement, exercise
4. seen more frequently in cats and horses than in dogs
5. may also see a lymphocytosis (epi-induced)

Question 8

describe absolute erythrocytosis

Answer 8

1. due to a true increase in RBC mass
   -all causes of a relative erythrocytosis must be excluded (calm, hydrated animal)
2. primary (rare): EPO independent (EPO is normal or low)
   -known as polycythemia vera: neoplastic proliferation of mature RBCs independent of EPO
   -RBCs are morphologically unremarkable
   -diagnosis of exclusion
3. secondary: EPO dependent (increased)
   a. appropriate: EPO production is increased secondary to hypoxia or hypoxemia
   -causes: heart disease, lung disease, high altitudes

b. inappropriate: EPO production increased without systemic hypoxia/hypoxemia
-causes: renal lesions causing local hypoxia, non-renal tumors that produce EPO or EPO-like substances, exogenous (doping)

Question 9

when would you aspirate a lymph node

Answer 9

1. lymphadenomegaly: enlargement of one or multiple lymph nodes
   -detected via palpation, radiography, or ultrasonography
2. eval for presence of metastatic disease/staging

Question 10

list the 6 commonly sampled lymph nodes, where they are located, and drainage features

Answer 10

1. mandibular: ventral angle of the jaw
   -drainage: most of the head, including rostral oral cavity
2. prescapular/superficial cervical: cranial shoulder
   -caudal part of the head (phraynx pinna), most of the thoracic limb and part of thoracic wall
3. axillary: caudal and medial to shoulder joint
   -most of thoracic wall, deep structures of the thoracic limb and neck, cranial mammary glands
4. superficial inguinal: furrow between abdominal wall and medial thigh
   -caudal mammary glands, ventral half of abdominal wall, penis, prepuce, scrotum, tail, ventral pelvis, medial thigh, stifle
5. popliteal: back of stifle
   -area distal to the stifle
6. medial iliac: near caudal vena cava and aorta (internal)
   –skin of pelvic area, pelvic limb distal intestinal and urogenital system

Question 11

describe making a diagnostic smear

Answer 11

1. goal: thin layer of intact cells, rapidly air-dried slides
2. methods: impression smears, woodpecker or needle off, fine needle non-aspirate, FNA
3. squash prep technique: allows for proper dispersion of cells and improves diagnostic ability
4. avoid making a splat or shotgun blast smears
   -limits diagnostic ability as it creates dense smears and high numbers of lysed cells

Question 12

describe sample eval

Answer 12

1. cellularity versus degree of blood contamination
2. eval cell types present, their morphology, and relative proportions of each cells type
3. determine if sample is actually lymph node
   -could be salivary epithelium if sample from mandibular lymph node
   -adipose tissue: if aspirated perinodal fat
   -could be muscle

Question 13

describe sizing of lymphocytes and cytomorphology

Answer 13

1. small lymphocytes:
   -smaller than a neutrophil, scant basophilic cytoplasm, condensed/closed chromatin with indistinct nucleoli
2. intermediate lymphocytes:
   -similar in size to a neutrophil, low to moderate amounts of basophilic cytoplasm, lighter chromatin
3. large lymphocyte:
   -larger in size than a neutrophil, low to moderate amounts of basophilic cytoplasm, finely stippled (open) chromatin often with visible nucleoli

Question 14

describe a normal lymph node

Answer 14

1. majority of small lymphocytes (>90%) with low numbers of intermediate and large lymphocytes (<10%)
2. low numbers of other cell types may also be present
   -macrophages: may contain hemosiderin (breakdown of heme pigment)
   -plasma cells: produce immunoglobulin
   -mast cells: should be individualized
3. lysed cells/artifact:
   -streaming nuclear debris or light pink nuclear fragments that lack cytoplasmic borders
4. lymphoglandular bodies: cytoplasmic fragments from lysed lymphocytes
   -routinely present in normal tissue but may be increased with lymphoma

Question 15

describe differentials for an enlarged lymph node

Answer 15

1. reactive or hyperplastic lymph npde
2. inflammation/lymphadenitis
3. neoplasia
   -primary: lymphoma
   -metastatic: carcinomas, other round cell tumors, melanoma, sarcomas

Question 16

describe a reactive lymph node

Answer 16

1. due to an antigenic response from local or generalize inflammation, infection, immune-mediated disease, or neoplasia
2. small lymphocytes predominate (>75%) but there are increased numbers of intermediated and large lymphocytes (>10% and up to 25%)
   -large lymphocytes 25-50% of population - grey zone
   -large lymphocytes >50% of population: lymphoma
3. plasma cells may be increased: variable numbers
4. may see Mott cells: plasma cells filled with immunoglobulin-containing vacuoles (called Russell bodies)

Question 17

describe lymphadenitis

Answer 17

1. inflammation within the lymph node
2. many causes: neutrophilic, eosinophilic, mixed
   -inflammatory cells may also be blood-associated: watch out for blood contamination!
   -predominant cel type categorizes the inflammation present

Question 18

describe neutrophilic lymphadenitis

Answer 18

1. may also be called purulent or supperative
2. > 5% neutrophils but exclude blood origin!!
3. fairly non-specific finding: may be associated with bacterial, neoplastic, or immune-mediated conditions
   -if mandibular lymph node: think dental disease

Question 19

describe (pyo)granulomatous lymphadenitis

Answer 19

1. called macrophagic or histiocytic lymphadenitis
2. increased numbers of macrophages (variable numbers)
3. pyogranulomatous = neutrophils and macrophages
4. causes:
   -chronic inflammation
   -higher order bacteria: filamentous, acid-fast
   -fungal infections

Question 20

describe eosinophilic lymphadenitis

Answer 20

1. greater then 3% eosinophils
2. several causes:
   -allergy/hypersensitivity
   -local skin disease (atopic dermatitis)
   -parasites (fleas)
   -some fungal infections (pythium)
   -paraneoplastic (lymphoma, MCT)

Question 21

describe mixed cell lymphadenitis

Answer 21

1. most common!
2. non-specific, can be due to a combination of etiologies

Question 22

describe lymphoma

Answer 22

1. characterized by a predominance of a monomorphic lymphocyte population that is >50% lymphocytes
2. most lymphomas are composed or large lymphocytes that exhibit atypia (open chromatin and predominant nucleoli)
   -small cell, well-differentiated variants exist and will require additional testing to diagnose
3. classified based on their immunophenotype (B versus T cell) which yields relevant treatment and/or prognostic info

Question 23

describe metastatic neoplasia

Answer 23

1. indicated by presence of a foreign cell population
2. usually of either epithelial (carcinoma) or round cell (LYMPH) origin
   -other tumor types may also metastasize to lymph nodes: melanoma, neuroendocrine tumors, sarcomas