Reactive Lymphadenitis - FNAC Microscopy

Smear Characteristics at Low Power

Cell Population (High Power)

1. Small Mature Lymphocytes (60-70%) - PREDOMINANT

• Round, regular nuclei
• Densely clumped (condensed) chromatin
• Scant cytoplasm
• These represent resting B and T lymphocytes

2. Medium Lymphocytes / Centrocytes (15-20%)

• Slightly larger than small lymphocytes
• More open chromatin
• Small indistinct nucleoli
• Represent follicle center cells

3. Large Transformed Lymphocytes / Immunoblasts (5-10%)

• Large cells with vesicular (open) chromatin
• Prominent central nucleolus
• Moderate to abundant basophilic cytoplasm
• Represent antigenically activated lymphocytes

4. Plasma Cells

• Eccentric, clock-face (cartwheel) chromatin
• Perinuclear hof (clear zone next to nucleus)
• Abundant basophilic cytoplasm
• Increased in viral infections and autoimmune conditions

5. Tingible Body Macrophages (TBM) - KEY FEATURE

• Large macrophages with phagocytosed nuclear debris (apoptotic fragments) in their cytoplasm
• These produce the "starry sky" appearance at low power
• Their presence indicates active germinal center reaction
• Characteristic of reactive hyperplasia (but also seen in high-grade lymphomas like Burkitt - a key differential)

6. Dendritic Lymphocytic Aggregates (Intact Follicles)

• Clusters of lymphoid cells around follicular dendritic cells
• Specific to reactive hyperplasia
• Not seen in lymphoma

7. Other Inflammatory Cells

• Neutrophils: Prominent in acute bacterial lymphadenitis - may infiltrate sinuses; in severe cases, pus cells predominate
• Eosinophils: Suggest parasitic infection, drug reaction, or Hodgkin lymphoma (if Reed-Sternberg cells also present)
• Mast cells: Scattered in reactive smears

Background Features

• Lymphoglandular bodies: Small, pale, anucleate cytoplasmic fragments present in the background - seen in ~86% of reactive lymphadenitis cases
• Capillary fragments: Often visible, supporting reactive/benign diagnosis
• No necrosis: Absence of necrotic background is a key feature (necrosis suggests TB, cat-scratch disease, or Kikuchi)

Pattern Variants Based on Cause

Key Differential: Reactive vs. Follicular Lymphoma (FL)

Diagnostic Report Summary

"Smears show a polymorphous lymphoid population comprising predominantly small mature lymphocytes admixed with centrocytes, immunoblasts, plasma cells, and tingible body macrophages. Dendritic-lymphocytic aggregates are noted. The background is clean with lymphoglandular bodies. No granulomas or necrosis. Features are consistent with reactive lymphoid hyperplasia."

• Robbins & Kumar Basic Pathology, Reactive Lymphadenitis section
• Histology: A Text and Atlas (Pawlina), Clinical Correlation on Reactive Lymphadenitis
• Stepwise approach to lymph node FNAC cytology (PMC, peer-reviewed)

Rabies Immunoglobulin (RIG) - Dose for 18.4 kg

Standard Doses (WHO / All Major Guidelines)

Volume to Draw Up

hRIG - Common formulations:

eRIG - Common formulations:

How to Administer

1. Infiltrate as much as anatomically possible directly into and around the wound site(s) - this is the priority
2. Remaining dose (if any cannot be infiltrated) - inject intramuscularly at a site distant from where the rabies vaccine will be given (e.g., anterolateral thigh)
3. Never inject RIG and rabies vaccine in the same syringe or same anatomical site
4. If the calculated dose is insufficient to cover all wounds, it may be diluted 2-3 fold with sterile normal saline to increase volume for wound infiltration

Critical Timing Rules

• Give RIG on Day 0 (same day as first vaccine dose) - ideally simultaneously but at different sites
• Can be given up to Day 7 after first vaccine dose if not available on Day 0
• Do NOT give after Day 7 - by then, active antibody response from the vaccine is already occurring and RIG will suppress it
• RIG is given only once - never repeated

Important Notes

• Do NOT exceed the calculated dose (20 IU/kg for hRIG) - excess RIG can paradoxically suppress the vaccine-induced immune response
• This dose applies to all age groups including children (no dose adjustment for pediatric patients)
• For previously vaccinated individuals - RIG is NOT indicated at all; only 2 doses of vaccine on Days 0 and 3
• eRIG no longer requires skin testing before administration (WHO 2018 position paper)

Clinical note: This information is for reference. Always confirm the exact vial concentration on the product label before drawing up the dose, as formulations vary by manufacturer and country.

Premi-Rab (Rabies Antiserum I.P.)

What is Premi-Rab?

Dose Calculation for 18.4 kg

Volume to draw up:

Administration Protocol (WHO 2018)

Step 1 - Wound infiltration (PRIMARY route)

• Inject as much of the 2.45 mL as anatomically possible directly into and around the wound(s)
• Use a fine needle; infiltrate to the depth of the wound
• For multiple wounds, divide the dose among all wound sites
• If volume is insufficient to cover all wounds, dilute 2-3x with sterile normal saline

Step 2 - Remaining dose

• Any RIG that cannot be safely infiltrated into the wound - inject intramuscularly at a distant site (e.g., anterolateral thigh), away from the vaccine injection site
• Never inject in the same site as the rabies vaccine

Key Rules

Side Effects to Watch

Note: Despite being equine-origin, modern highly purified eRIG (including Premi-Rab) carries only a very small anaphylaxis risk. Always have epinephrine 1:1000 and resuscitation equipment ready.

Summary for 18.4 kg Patient Using Premi-Rab 300 IU/mL

Draw 2.45 mL from the 5 mL vial. Infiltrate the entire dose into and around the wound site. Give simultaneously with the first dose of rabies vaccine at a different anatomical site.

⚕ Always confirm the concentration printed on the vial label before drawing up - Premi-Rab is available in both 200 IU/mL and 300 IU/mL formulations.