Diseases of cutaneous appendages

Published on 08/03/2015 by admin

Filed under Pathology

Last modified 22/04/2025

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15 Diseases of Cutaneous Appendages

Hair basics 298
INFLAMMATORY DISEASES OF THE PILOSEBACEOUS APPARATUS 299
Acneiform lesions 299

Acne vulgaris 299
Neonatal cephalic pustulosis 300
Acne fulminans 300
Chloracne 300

Superficial folliculitides 301

Acute superficial folliculitis 301
Actinic folliculitis 301
Acne necrotica 301
Acne necrotica miliaris 301
Necrotizing folliculitis of AIDS 301
Eosinophilic folliculitis 302
Infundibulofolliculitis 303

Deep infectious folliculitides 303

Furuncle 303
Pseudomonas folliculitis 303
Gram-negative folliculitis 303
Viral folliculitis 304
Dermatophyte folliculitis 304
Pityrosporum folliculitis 304

Deep scarring folliculitides 305

Folliculitis decalvans 305
Folliculitis keloidalis nuchae 305

Follicular occlusion triad 306

Hidradenitis suppurativa 306
Dissecting cellulitis of the scalp 307
Acne conglobata 307

Miscellaneous folliculitides 308

Pseudofolliculitis barbae 308
Pruritic folliculitis of pregnancy 308
Perforating folliculitis 309
Follicular toxic pustuloderma 309
Sterile neutrophilic folliculitis with
perifollicular vasculopathy 309
Pseudolymphomatous
folliculitis 309

HAIR SHAFT ABNORMALITIES 310
Fractures of the hair shaft 310

Trichorrhexis nodosa 310
Trichoschisis 310
Trichothiodystrophy 310
Trichoclasis 310
Trichorrhexis invaginata 310
Tapered fractures 310
Trichoptilosis 310
Trichoteiromania 310
Trichotemnomania 310

Irregularities/abnormalities of hair shafts 311

Pili canaliculi et trianguli 311
Pili bifurcati 311
Pili multigemini 311
Trichostasis spinulosa 311
Pili annulati 311
Monilethrix 312
Tapered hairs 312
Bubble hair 312
Trichomegaly 312

Coiling and twisting abnormalities 312

Pili torti 312
Woolly hair 312
Acquired progressive kinking 313
Circle hair, rolled hair and trichonodosis 313

Extraneous matter on hair shafts 313

Tinea capitis 313
Black piedra 313
White piedra 313
Trichomycosis axillaris 314
Pediculosis capitis 314
Hair casts 314
Deposits 314

ALOPECIAS 315
Basic hair stages 315

Anagen stage 315
Catagen stage 315
Telogen stage 316

Congenital and hereditary alopecias 316

Alopecia universalis congenita 316
Hereditary hypotrichosis 316
Atrichia with papular lesions 316
Keratosis pilaris atrophicans 316
Hallermann-Streiff syndrome 316
Short anagen syndrome 317

Premature catagen/telogen 317

Trichotillomania and traumatic alopecia 317
Telogen effluvium 317

Premature telogen with anagen arrest 318

Alopecia areata 318

Vellus follicle formation 319

Androgenic alopecia 319
Temporal triangular alopecia 319

Anagen effluvium 320

Loose anagen syndrome 320
Drug-induced alopecia 320

Scarring alopecias 320

Idiopathic scarring alopecia 320
Traction alopecia with scarring 320
Postmenopausal frontal fibrosing alopecia 320
Fibrosing alopecia in a pattern distribution 320
Folliculitis decalvans 320
Central centrifugal cicatricial alopecia 321
Tufted-hair folliculitis 321

Miscellaneous alopecias 321

Lipedematous alopecia 321

MISCELLANEOUS DISORDERS 322
Pilosebaceous disorders 322

Hypertrichosis 322
Keratosis pilaris 322
Keratosis pilaris atrophicans 323
Follicular spicules 323
Lichen spinulosus 323
Rosacea 324
Pyoderma faciale 324
Squamous metaplasia of sebaceous glands 324
Neutrophilic sebaceous adenitis 324
Follicular sebaceous casts 324

Apocrine disorders 325

Fox-Fordyce disease 325
Apocrine chromhidrosis 325

Eccrine disorders 326

Eccrine duct hyperplasia 326
Syringolymphoid hyperplasia 326
Eccrine metaplasia 326
Neutrophilic eccrine hidradenitis 326
Palmoplantar eccrine hidradenitis 326
Sweat gland necrosis 326

Vestibular gland disorders 326

Vulvar vestibulitis 326

Endothrix infection

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Hair basics

Hair follicle formation:

• By 18th week, hair on entire body (except palms/soles/genitalia)
• Growth rate = 1 mm every 3 days (or 0.35-0.37 mm/day), or 1 cm per month
• Lose an average of 50-100 hairs per day

Pigment predominantly in cortex layer:

• Eumelanin = brown/black hair
• Pheomelanin = red/blonde hair: red hair often has variant to MC1R gene (melanocortin receptor)

Three stages of hair cycle (discussed further under “Alopecia” on p. 315):

1 Anagen (growth phase; years; 85% of hair follicles)
2 Catagen (degenerative/transition from growth-to-resting phase, weeks)
3 Telogen (resting, months)

• Sonic Hedgehog (Shh), a signaling molecule, appears to mediate the transition from telogen to anagen

Three zones of hair follicle (superficial-to-deep):

1 Infundibulum = ostium to sebaceous duct opening
2 Isthmus = sebaceous duct to insertion of arrector pili muscle
3 Inferior segment = below insertion of muscle:

– contains bulb (or matrix) and stem
– Adamson’s fringe = level where hair cornification starts; below area, the hair bulb is mitotically active

Hair layers (in order of “inner-to-outer”):

• Medulla (central part of hair fiber) = contains citrulline:

– vellus hairs have no medulla

• Hair cuticle = outer layer of hair shaft
• Inner root sheath (IRS) = function is to mold hair by hardening filaments and decomposes around sebaceous gland duct level; contains trichohyalin granules:

– three components of IRS = cuticle of IRS (innermost), Huxley’s layer, and Henle’s layer (outermost, keratinizes first)

• Outer root sheath (ORS) = characterized by trichilemmal keratinization; forms outer cylinder of hair follicle (merges into epidermis and hair bulb at each end):

– bulge = segment of ORS near arrector pili insertion; major area of epithelial stem cells of the hair follicle; cells below bulge degenerate in catagen and telogen stages

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