Pediculosis

Pediculosis: Overview & Etiology - Lice Life Lowdown

• Definition: Ectoparasitic infestation by lice (Order: Anoplura).
• Etiologic Agents:
  • Pediculus humanus capitis (Head louse)
  • Pediculus humanus corporis (Body louse)
  • Pthirus pubis (Pubic/Crab louse)
• Life Cycle: Egg (Nit) → Nymph (3 instars) → Adult.
  • Nits: Oval, <1mm, firmly attached to hair shafts. Hatch in 7-10 days.
  • Adults: Obligate human parasites, live ~30 days on host; die in 1-2 days off-host.

⭐ Pediculus humanus capitis is the most common ectoparasitic infestation in children worldwide.

Pediculosis: Clinical Features - Itch & Scratch Saga

• Cardinal symptom: Pruritus (itching), often intense, leading to scratching.
• Caused by hypersensitivity to louse saliva.

Pediculosis Capitis (Head Lice):

• Scalp pruritus: esp. occipital & post-auricular areas.
• Visible nits (eggs) on hair shafts; adult lice less common.
• Excoriations, secondary impetiginization, cervical lymphadenopathy.

Pediculosis Corporis (Body Lice):

• Pruritus: trunk, axillae, shoulders (areas covered by clothing).
• Lice/nits in clothing seams.
• Linear excoriations, post-inflammatory hyperpigmentation (Vagabond's disease).
• ⭐ > Pediculosis corporis uniquely transmits epidemic typhus (Rickettsia prowazekii), trench fever (Bartonella quintana), and relapsing fever (Borrelia recurrentis).

Pediculosis Pubis (Phthiriasis/Crab Lice):

• Pubic/perineal pruritus; may affect axillae, chest hair, eyelashes (pediculosis ciliaris).
• Maculae ceruleae: pathognomonic bluish-grey macules at feeding sites.
• Nits on hair; adult lice may be seen at hair base.
• Often sexually transmitted; screen for other STIs.

Pediculosis: Diagnosis & Differentials - Louse Clues & Lookalikes

• Diagnosis
  • Visual inspection: Direct sight of live lice or nits (eggs). Nits are oval, grayish-white, firmly attached to hair shafts.
  • Wood's lamp: Live nits may fluoresce pale blue; not consistently reliable.
  • Dermoscopy (trichoscopy): Magnified view aids identification of lice, nits, and empty eggshells. Differentiates nits from pseudonits.

• Differential Diagnoses
  • Seborrheic dermatitis: Greasy scales, erythema, often diffuse.
  • Tinea capitis: Fungal infection; broken hairs, scaling, alopecia.
  • Hair casts/Peripilar keratin casts: White, circumferential accretions that slide easily along hair (unlike nits).
  • Piedra: Fungal infection forming hard nodules on hair.
  • Booklice (Psocoptera): Environmental contaminants, not true lice.

⭐ Nits found more than 1 cm from the scalp are generally considered non-viable or hatched, as they require warmth from the scalp for incubation.

Pediculosis: Management & Prevention - Nixing Nasty Nits

Key Pediculicides:

*   Wet comb q2-3d for 2 wks.
*   Wash fomites (clothing, bedding) in hot water (>**55°C**); dry on hot.
*   Seal non-washables (2 wks) or freeze.

• Prevention:
  • Avoid head-to-head contact.
  • Screen & treat contacts.

Treatment Algorithm: Pediculosis Capitis

⭐ First-line treatment for pediculosis capitis is typically topical Permethrin 1% or Malathion 0.5%; oral Ivermectin is reserved for resistant/severe cases or when topical application is impractical.

High‑Yield Points - ⚡ Biggest Takeaways

• Head lice (capitis): Common in children; intense scalp itching (occipital, post-auricular); nits on hair.
• Body lice (corporis): Linked to poor hygiene; lice in clothing seams; vector for typhus, trench fever.
• Pubic lice (pthiriasis): Sexually transmitted; severe pubic itching; maculae ceruleae are characteristic.
• Diagnosis: Visualisation of live lice or viable nits near scalp.
• Treatment: Topical permethrin is first-line; oral ivermectin is an alternative. Treat contacts and fomites.
• Eyelash involvement: Treat with petrolatum ointment.