# Management of plica polonica in the wake of refractory head lice infestation: a case report

## TL;DR

A case report shows that head lice resistant to chemicals can lead to severe infestations, requiring physical treatments for resolution.

## Contribution

This case highlights the challenges of treating head lice with resistance genes and the effectiveness of physical treatment methods.

## Key findings

- A 13-year-old girl's head lice infestation progressed to plica polonica due to resistant lice.
- Lice sampled showed a 100% homozygous knockdown resistance (kdr) mutation.
- Physical treatment methods were effective when chemical treatments failed.

## Abstract

Pediculosis capitis remains widespread globally, and the emergence of resistance genes continues to impede eradication efforts. This case of plica polonica offers insight into the complexity and challenges of pediculosis in endemic settings where resistant lice are present.

We report the case of a 13-year-old girl from a suburban area of Bangkok with long-standing pediculosis that progressed to plica polonica due to prolonged lack of intervention. Molecular analysis of the sampled lice demonstrated a 100% homozygous knockdown resistance (kdr) mutation. Several of her classmates also described recurrent infestations despite previous permethrin use, and permethrin exposure in this case showed limited effect, as lice remained viable after the recommended treatment period. The condition resolved after incorporating physical modalities.

Pediculosis in endemic areas is at a high suspicion for resistance. Chemical treatment alone may not lead to a cure, and caretakers should emphasize other treatment forms to achieve a cure. Such an approach may help prevent further mutations due to inbreeding within the headlice population with resistance genes from the unoptimized chemical treatment.