Non-malignant skin disease

Non-malignant skin disease is relatively common. The pathology may or may not be specific. Some diseases require clinical information to diagnose.

General classification (Inflammatory)

• Bullous.
• Interface.
• Nodular & diffuse.
• Spongiotic.
• Vasculitis.
• Perivascular.
• Panniculitis.
• Psoriasiform.

Tabular comparison of inflammatory skin disease (adapted from Brister):

Pattern	Key histologic feature	Subclassifications	Example
Bullous	"Empty space"	-Subcorneal -Suprabasillar -Subepidermal	-? -? -?
Interface	Inflammation at DE junction	-Vacuolar (minimal) -Lichenoid (band-like)	-Erythema multiforme -Lichen simplex chronicus (LSC)
Nodular & diffuse	Nodular & diffuse	?
Spongiotic	Edema between keratinocytes	-Acute -Subacute -Chronic	-Poison Ivy -Nummular dermatitis -Atopic dermatitis
Vasculitis	Inflammation of vessel wall	?	?
Perivascular	Inflammation around vessels	?	?
Panniculitis	Inflamm. of SC tissue	-Septal -Nodular
Psoriasiform	Epidermal thickening and long rete ridges	-Regular -Irregular

Notes:

• DE junction = dermal-epidermal junction.
• The "empty space" in bullous disease in situ is filled with fluid.

Lichen planus

• Oral pathology.

Microscopy

Features:

• Loss of rete ridges.
• Loss of basal cells (stratum basale).
• Interface dermatitis (lymphocytes at dermal-epidermal junction).

Ref.: http://emedicine.medscape.com/article/1078327-overview.

Lichen sclerosus

• AKA chronic atrophic vulvitis (when vulvar lesion).

Etiology

• Scratching due to pruritis.

Histology

Key feature:

• Subepithelial fibrosis.

Lichen simplex chronicus

Histology

Key features:

• Acanthosis (epithelial thickening).
• Hyperkeratosis.

Seborrheic keratosis

General

• Benign.
• Common.

Epidemiology

• Old people.

Gross

• "Stuck-on" appearance - raised lesion.

Image(s):

• SK - gross image (dermatlas.org).

Microscopic

Features:

• Normal appearing epidermis - raised above skin surface.
• "Horn cysts" - collections of keratin.

Image(s):

• Seborrheic keratosis (WC)

Molluscum contagiosum

• Etiology: caused by molluscum contagiosum virus.

Micro

• A suprabasilar epidermal lesion consisting of "molluscum bodies", i.e. molluscum bodies are found above the stratum basale.
• Molluscum bodies:
  • Large cells with abundant granular eosinophilic cytoplasm.
  • Small peripheral nucleus.

Note:

• Molluscum bodies vaguely resemble signet ring cells -- but:
  • Cytoplasm eosinophilic and granular.
  • Nucleus usually smaller than in signet ring cell.
  • Molluscum bodies are only the epidermis - an uncommon place to find SRCs without finding them elsewhere.
• The granular eosinophilic cytoplasm represents accumulated virons.

Dermal nevus

• Think melanoma.

Clinical: ABCD = asymmetric, borders (irregular), colour (black), diameter (large).

Micro

Features:

• Symmetrical lesion.
• "Matures" with depth - less cellular, less atypia.
• No destruction of surrounding structures.
• Only in dermis key feature.
  • Otherwise it is something else, e.g. dermal nevus, junctional nevus.

Microscopic

• Basaloid cells mixed with squamous cells.
• Keratin-filled invaginations.
• Horn cysts - intraepidermal, brown globule-like structures.
  • Melanocytes at the dermoepidermal junction.

Images:

• SK - wikimedia.org.
• SK - high mag. - dermatlas.org.
• SK - low mag. - dermatlas.org.

Pilomatrixoma

General

• Benign skin tumour.
• Most common solid skin tumour of children.

Clinical:

• Hard nodule - calcification.
• +/-Painful. (???)

Treatment:

• Surgical excision.

Microscopic

Features:

• Location: lower dermis/subcutaneous fat; thus, usu. surrounded by connective tissue.
• Sharpy demarcated island of cells.
• Calcification in 75% - with calcium staining (von Kossa).
• Cells:
  • Basaloid epithelial cells - have prominent nucleoli.
  • Anucleate squamous cells ("ghost cells").
• Giant cell foreign body type granulomas (form in reaction to keratin).

Notes:

• Keratin a prominent feature on cytology - lots of orange stuff.

Images:

• Pilomatrixoma (bccancer.bc.ca).

DDx:

• Epidermal inclusion cyst.

Syringoma

• Benign sweat duct tumour. (???)
• Eccrine differentiation.

Microscopic

Features:

• Proliferation of benign ducts with lined by a bilayer (as in normal sweat ducts) with abnormal architecture:
  • Tadpole like appearing ducts.

Image:

• Syringoma (flickr.com).

Inverted follicular keratosis

• Benign skin lesions.
  • May mimic squamous cell carcinoma or basal cell carcinoma.

Images:

• Inverted follicular keratosis - low mag. (flickr.com).
• Inverted follicular keratosis - high mag. (flickr.com).

Keratoacanthoma

• Abbreviated KA.
• Generally considered to be benign.
  • Rare reports of metastases suggesting it may be a form of squamous cell carcinoma.

Clinical

• May grow rapidly (weeks or months) then involute.
• Main DDx is squamous cell carcinoma.
• Exophytic lesion, well-circumscribed.

Microscopic

Features:

• Expansion of stratum spinosum - pushing tongue-like downward growth of epidermis into the dermis.
• Keratin collection (keratin plug) at the center of lesion-superficial aspect.
• Cells have glassy pink cytoplasm.
• Minimal/no nuclear atypia.

Image:

• Keratocanthoma (WC).

Bullous disease

Main article: Bullous disease

Cysts

Main article: Dermal cysts

See also

• Dermatopathology introduction.
• Malignant skin disease.