Common Rashes

Question 1

Pathogenesis of acne

Answer 1

Blockage of pilosebaceous follicles due to abnormal keratinisation and increased production of sebum –> comedones.

Blockage alters microbiome –> proliferation of Cutibacterium acnes –> activates innate immune system –> inflammatory response –> neutrophil recruitment –> elastase production –> connective tissue damage

Scarring and post inflammatory hyperpigmentation follow.

Question 2

Clinical features of acne

Answer 2

Face and upper torso affected.
Skin becomes greasy (seborrhoea).
Lesions are:
- non inflammatory = open comedones (blackheads) or closed comedones (whiteheads)
- inflammatory = papules, pustules, nodules and cysts
- scars = raised (hypertrophic) or depressed/ pitted

Question 3

Acne associated auto inflammatory syndromes

Answer 3

Severe acne associated with auto inflammatory syndromes causing fever and systemic inflammation.

Examples:
Pyoderma gangrenosum
SAPHO syndrome = synovitis, acne, pustulosis, hyperostosis, osteitis
PAPA = pyoderma grangrenosum, acne, pyogenic arthritis

Question 4

Management of acne

Answer 4

Need to determine whether inflammatory or non inflammatory lesions predominate. Key is to prevent scar formation

1st line = topical non antibiotic therapy + oral tetracycline/ erythromycin

• e.g. topical retinoids, azelaic acid, salicylic acid and benzoyl peroxide (all are keratolytic)
• oil free moisturiser often needed as agents cause dry skin
• avoid prolonged antibiotics (promote resistance) and should not be used without non antibiotic therapy

Females = COC + cyproterone acetate (a mild antiandrogen) reduce sebum concentration

• low dose spironolactone can be helpful
• avoid progesterone only pills as they exacerbate acne

Severe inflammation +/- scarring or milder cases with psychological upset = isotretinoin

Question 5

Side effects of isotretinoin

Answer 5

Dryness of mucous membranes
Teratogenicity (females of child bearing age MUST be on contraception)
Depression and increased suicide risk

Question 6

Hidradenitis suppurativa (HS)

Answer 6

“Acne inversa”
= chronic inflammatory disorder affecting apocrine pilosebaceous follicles of the axilla, inguinal area and under the breasts

Causes recurrent abscesses, draining sinuses, and scarring.

Question 7

Associations of hidradenitis suppurativa

Answer 7

Obesity
Metabolic syndrome
Smoking

Question 8

Management of HS

Answer 8

Bacterial biofilms within occluded follicles may explain disappointing results of antibiotics.

Options include oral tetracycline, combined rifampicin and clindamycin, acitretin and adalimumab (anti-TNF).

Surgery may be needed to drain abscesses

Question 9

Acne excoriee

Answer 9

Acne variant (less common cf. rosacea)
Mainly young women who pick mild acne spots –> prominent excoriations
Usually underlying psychological upset