Lingua villosa nigra (black hairy tongue) in a 2-week-old newborn

A two-week-old term male was brought to a primary care appointment for a routine health assessment. Birth history was unremarkable. The patient was exclusively breastfed up to 7 days of life, when artificial formula was started due to apparent insatiability. No feeding difficulties were noted, and median weight gain was 42 g/day since birth. He was receiving supplementation with 667 UI of cholecalciferol daily and parents denied any other supplementation or off-label drugs. Physical examination was unremarkable except for a brown lesion with irregular borders located on the posterior two-thirds of the tongue dorsum (Figure 1). Parents had not noticed the presence of this lesion prior to the appointment and had no knowledge of similar cases in the family.

Figure 1. Newborn’s black hairy tongue.


What is the diagnosis?