Alopecia as a systemic disease.

Alopecia is a skin condition of great social and psychologic impact. Primary alopecia originates from the hair follicles and usually does not have systemic manifestations; however, secondary alopecia can affect the hair follicles in the setting of systemic diseases, medications, and external trauma. Connective tissue diseases, granulomatous diseases, bullous diseases, infections, and tumors are some of the systemic diseases that will be covered in this review. Trichoscopy is a useful noninvasive tool that can help with the diagnosis in the office and can guide the selection of the optimal site for the scalp biopsy. Histopathology is the ultimate tool for the diagnosis in most cases of secondary alopecia and can be performed on vertical and horizontal sections. In most cases, treating the underlying condition is the single most important strategy, but topical treatments for the alopecia are also applied.