Pediculosis — SAQ

Stem

A 7-year-old girl presents to her GP with a 3-week history of scalp itch, worse behind the ears and at the nape of the neck. The mother has noticed "white specks" in the hair and a few crusty yellow areas on the scalp. Several classmates have similar symptoms. The girl is otherwise well, is up to date with immunisations, and has no drug allergies.

On examination, occipital and post-auricular lymphadenopathy is palpable, and there are excoriations and a few crusted yellow areas (honey-coloured) suggestive of impetigo. Detection combing of damp hair yields several live lice and nits close to the scalp.^[2]

Tasks:

a) What is the most likely diagnosis, and what features support it? (2 marks)

b) What is the differential diagnosis for the white specks in the hair, and how do you confirm the diagnosis? (2 marks)

c) Outline your stepwise management of this child, including treatment of the infestation, the secondary infection, the household contacts, and the school. (4 marks)

^[1][3]d) What advice would you give the family about prevention of recurrence and when the child can return to school? (2 marks)

Model answer

a) Most likely diagnosis and supporting features (2 marks)

• Pediculosis capitis (head lice) with secondary impetiginisation of excoriations.
• Supporting features: scalp pruritus worse over occiput, post-auricular area, and nape (typical distribution); detection combing showing live lice and nits close to the scalp; close contact with affected classmates (head-to-head transmission); occipital/post-auricular lymphadenopathy; secondary impetigo (honey-coloured crusts) from excoriation.

^[2]

^[2]b) Differential and confirmation (2 marks)

• Differential for white specks on hair: dandruff/seborrhoeic dermatitis (loose, slides), hair casts / pseudo-nits (keratin cylinders that slide), white piedra (Trichosporon, soft white nodule, KOH positive), black piedra (Piedraia, hard black nodule), trichorrhexis nodosa (fracture nodes), monilethrix (beaded hair).
• Confirmation: nits are firmly cemented to the hair shaft by chitin glue and do not slide (dandruff and hair casts slide). Wood's lamp (live nits fluoresce pale blue). Dermoscopy (10-30x) visualises the louse. Microscopy of plucked hair in 10% KOH confirms a viable egg (embryo visible) vs empty shell.

c) Stepwise management (4 marks)

• Infestation: First-line dimeticone 4% lotion (preferred for no resistance and safety) OR permethrin 1% cream rinse, applied per manufacturer instructions, repeated at day 7 (two applications are required because no agent is 100% ovicidal). Fine-toothed detection comb on damp, conditioned hair after each application.
• Secondary impetigo: oral flucloxacillin per local guidance (or clarithromycin if penicillin-allergic). Local wound care; topical mupirocin if localised.
• Household contacts: examine and treat affected household members at the same time. Hot-wash bedding, towels, hats, and combs; seal soft toys for two weeks. No need for insecticidal sprays.
• School: no exclusion is typically required once treatment has started — check local school guidance on "no-nit" policies. Advise the school nurse so that other cases can be identified and treated.

^{[1] [2]}

^[1]d) Prevention of recurrence and school return (2 marks)

• Treat all household contacts at the same time (the commonest cause of recurrence is re-infestation from an untreated carrier).
• Detection combing weekly for 2-3 weeks after treatment; a single live louse warrants re-treatment.
• Avoid head-to-head contact at school and play (long hair tied back; discourage sharing of combs, hats, headphones).
• No "no-nit" exclusion — return to school once treatment has started, per local school guidance. Continue combing; residual empty nits can be removed with fingers or a fine comb but are not a reason for exclusion.
• Watch for signs of resistance if live lice persist after two correctly-applied courses — switch to a different class (dimeticone to malathion, or permethrin to oral ivermectin per local protocol).

^{[1] [2]}

References3ShowHide

1. [1]Burgess IF, Brown CM, Lee PN. Treatment of head louse infestation with 4 percent dimeticone lotion: randomised controlled equivalence trial BMJ, 2005.PMID 15951310
2. [2]Meinking TL. Clinical update on resistance and treatment of Pediculosis capitis Am J Manag Care, 2004.PMID 15515630
3. [3]Burgess IF, Brown CM, Lee PN. Treatment of head louse infestation with 4 percent dimeticone lotion: randomised controlled equivalence trial BMJ, 2005.PMID 15951310