A 25-year-old woman presented with generalized pruritus not responsive to antihistamines and topical steroids. Examination showed excoriated papules on the limbs and a whitish scale between the toes. Dermatoscopy revealed the typical “triangle sign,” which corresponds to the anterior mite (Fig. 1a). A burrow ink test (BIT) was positive and showed a classic S-shaped burrow (Fig. 1b). Dermatoscopy of BIT showed the Sarcoptes scabiei’s eggs (Fig. 1c). The patient and contacts were successfully treated with topical permethrin cream.

Figure 1
figure 1

Panel a Classic dermatoscopy image of “triangle sign”, which corresponds to the anterior part of the mite (black arrows). Magnification × 10. Panel b Burrow ink test: staining of the same lesion with washable blue ink. Without magnification, a clear outline and classic S-shaped burrow. Panel c Polarized dermatoscopy (× 10) after ink staining. The “mother” mite is visible to the extreme side of the burrow (black arrow). Also, many eggs are evident (short red arrows).

Full size image

The BIT is a simple test to diagnose scabies. It is performed by rubbing a suspected burrow with ink from a marking pen. Excess ink is wiped off with an alcohol swab. If a mite burrow is present, the ink will fill the burrow in the stratum corneum, where the mite has tunneled, revealing the characteristic S-shaped burrow1.

The gold standard diagnostic test remains biopsy. In one study comparing the BIT to shave biopsy (n = 55), 36% of BIT-negative lesions had confirmed scabies-positive infections by biopsy2.

Due to the paucity of mites in many cases, a negative BIT does not rule out infection. However, the BIT should be considered a non-invasive, inexpensive, easy-to-perform test for scabies diagnosis, not requiring special equipment or training.3