A 19-year-old woman presents with intense nocturnal pruritus affecting her interdigital spaces, wrists, and axillary folds. Her college roommate has similar complaints. On dermoscopy, a triangular structure resembling a 'hang-glider' or 'delta wing' is seen at the end of a burrow. What is the causative agent and the drug of choice?

• A Pediculus humanus capitis; malathion 0.5% lotion
• B Demodex folliculorum; metronidazole gel
• C Sarcoptes scabiei var. hominis; benzyl benzoate 25%
• D Sarcoptes scabiei var. hominis; permethrin 5% cream ✓

Explanation

Scabies is caused by Sarcoptes scabiei var. hominis, an obligate human ectoparasite. The pathognomonic dermoscopic sign is the 'delta wing jet' or 'hang-glider' sign, representing the mite's body and forelegs at the closed end of a burrow. Nocturnal pruritus and involvement of close contacts are classic features. Permethrin 5% cream applied from neck to toe and washed after 8–12 hours is the current drug of choice due to its efficacy and safety profile, including in pregnancy. Benzyl benzoate 25% is an older alternative associated with more irritation.

Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.