The correct answer is B. Erosive pustular dermatosis.
Erosive pustular dermatosis of the scalp (EPDS) is a rare, inflammatory, and chronic slow-onset disease that causes scarring alopecia and mainly affects the scalp of older men. Clinical diagnosis can be challenging since it mimics more common diseases and due to its nonspecific clinical features. Different histologic findings can be seen depending on the stage of disease, with EPDS potentially being characterized by an atrophic epidermis and chronic inflammation consisting of lymphocytes, neutrophils, and occasional foreign body giant cells. Dermoscopy (or trichoscopy) has been recently reported as a useful aid for the diagnosis, as it shows absent follicular ostia with marked skin atrophy, with consequent visualization of dermal vessels, although histology is mandatory for the final diagnosis.
The remaining answer choices are reasonable to include on the differential diagnosis, but the clinico-pathologic findings are most supportive of EPDS.