What is the most likely diagnosis for a 16-year-old girl with non-scaly, discrete hair loss areas and a history of atopic eczema?

The clinical presentation of non-scaly, discrete areas of hair loss, particularly in a 16-year-old girl with a history of atopic eczema, strongly suggests alopecia areata. This autoimmune condition is characterized by sudden, patchy hair loss and can occur in individuals with other atopic conditions, like eczema or asthma.

In this case, the absence of scaling and the distinct patches of hair loss further support the diagnosis of alopecia areata rather than other conditions such as hypothyroidism, lupus erythematosus, or trichotillomania.

Hypothyroidism typically presents with diffuse hair thinning rather than discrete patches, and it is usually accompanied by other systemic symptoms such as weight gain, fatigue, and cold intolerance. Lupus erythematosus can lead to hair loss, but it is often associated with a characteristic rash or systemic signs, which are not indicated in this scenario. Lastly, trichotillomania involves habitual hair pulling, which is usually accompanied by signs of distress and can lead to broken hair rather than pure patchy loss.

Thus, the combination of a young female patient with patchy hair loss and a history of atopic eczema points to alopecia areata as the most likely diagnosis