What is a pathognomonic physical finding of pediculosis and pthiriasis (lice infestation)?

Updated: Aug 16, 2019
  • Author: Lyn C C Guenther, MD, FRCPC, FAAD; Chief Editor: Michael Stuart Bronze, MD  more...
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The finding of maculae cerulea is believed to be pathognomonic for infestation with lice. Maculae cerulea are blue-gray macules, which are actually a discoloration of the skin due to the insect's bite. Enzymes in the louse saliva are believed to induce the breakdown of human bilirubin to biliverdin, causing the change in skin color associated with maculae cerulea. An allergic reaction to louse bites may result in intense itching. Secondary infections due to excoriations may occur.

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