1) Core orientation for screening (both types)

1. Scan at low power first
   • Epidermal thickness/pattern (regular, psoriasiform, atrophic, acanthotic)
   • Stratum corneum type (orthokeratosis/parakeratosis; compact/loose)
   • Dermoepidermal junction contour (rete ridges present/absent, elongation)
   • Distribution of inflammation (superficial, deep, periappendageal, perivascular, lichenoid, interface, diffuse)
   • Presence/absence of adnexa (hair follicles, sebaceous glands, eccrine units)
2. Then high power
   • Keratinocyte maturation, spongiosis, dyskeratosis, cytologic atypia
   • Basal layer change and pigment transfer
   • Inflammatory cell type
   • Vessel/endothelial changes
   • Neural/mechanoreceptor structures (if present)

2) Thick skin histology (palms/soles)

A. Epidermis

• Very thick epidermis, especially:
  • Stratum corneum: markedly thick, compact orthokeratosis
  • Stratum lucidum: distinct eosinophilic translucent band (key feature)
  • Stratum granulosum: prominent
  • Stratum spinosum: well-developed
• Rete ridges: deep and often regular; pronounced interdigitation with dermal papillae
• No hair follicles, no sebaceous glands, no apocrine glands

B. Dermis and adnexa

• Dense papillary and reticular dermis
• Abundant eccrine sweat glands/ducts (acrosyringia visible traversing epidermis)
• Mechanoreceptors may be conspicuous:
  • Meissner corpuscles in dermal papillae
  • Pacinian corpuscles deeper dermis/subcutis (especially volar skin)

C. Histopath screening cues in thick skin biopsies

• Hyperkeratotic lesions can appear “exaggerated” due to baseline thick SC
• Don’t overcall pathologic acanthosis without comparing to expected thick-skin baseline
• Focus on:
  • Cornoid/keratin abnormalities pattern
  • Acral-specific interface changes
  • Eccrine-centered pathology (e.g., neutrophils in acrosyringium for palmoplantar pustular processes)

3) Thin skin histology (most body surface)

A. Epidermis

• Thinner epidermis
• Stratum corneum: relatively thin
• Stratum lucidum: absent
• Stratum granulosum: thinner/less prominent than thick skin
• Rete ridges usually less deep and more variable by site

B. Dermis and adnexa

• Hair follicles present
• Sebaceous glands present (except certain regions)
• Eccrine glands present but less dominant than in thick skin
• Apocrine units in site-specific areas (axilla, anogenital, areola)

C. Histopath screening cues in thin skin biopsies

• Follicular and sebaceous pathology becomes central:
  • Folliculitis patterns
  • Perifollicular fibrosis/inflammation
  • Sebaceous alteration
• Interface and adnexotropic infiltrates easier to localize to follicular units
• Atrophy is easier to appreciate due to thinner baseline epidermis

4) Side-by-side “must know” comparison table

5) Practical histopathology screening algorithm (dermatopath)

1. Identify site phenotype first: thick vs thin skin
2. Confirm expected adnexa:
   • If acral sample shows follicles/sebaceous glands, question specimen labeling or site mix
3. Assess epidermal reaction pattern:
   • Spongiotic, psoriasiform, lichenoid/interface, vesiculobullous, granulomatous surrogate signs
4. Assess cornification pattern:
   • Orthokeratosis/parakeratosis, compactness, focal columns, neutrophils in cornified layer
5. Assess appendageal involvement (thin skin especially):
   • Perifollicular, intrafollicular, peri-eccrine
6. Assess dermal inflammation pattern and depth
7. Correlate with site-adjusted normal baseline before calling abnormal

6) Common pitfalls in thick vs thin skin interpretation

• Acral skin:
  • Baseline thick SC and acanthosis can mimic chronic dermatitis/psoriasiform change
  • Eccrine duct prominence can be misread as adnexal proliferation
• Thin skin:
  • Tangential sectioning can falsely suggest epidermal thinning or rete flattening
  • Follicular dropout in scarred areas can be mistaken for naturally non-follicular skin
• Both:
  • Poor orientation and crush artifact create false interface/spongiotic impressions

7) Reporting template (screening level)

• Specimen type/site: compatible with thick vs thin skin features
• Epidermis: thickness, keratinization pattern, granular/lucidum status, rete pattern
• Adnexa: follicles/sebaceous/eccrine/apocrine presence and involvement
• Dermis: inflammatory pattern, depth, vessel changes, fibrosis, edema
• Provisional pattern diagnosis: e.g., spongiotic dermatitis pattern, lichenoid/interface pattern
• Site-adjusted comment: note acral baseline if thick skin