• A history of external stress on the hair—thermal, traction, or chemical—along with broken hair shafts following the hair pull test support the diagnosis of acquired trichorrhexis nodosa.
Diagnostic clues for focal or patchy alopecia include:
• Alopecia areata generally presents as focal hair loss in an annular distribution; pruritus, erythema, and scale are absent.
• Seborrheic dermatitis can present as pruritic erythematous patches with scale distributed on the scalp and, in some cases, in the eyebrows, nasolabial folds, or paranasal skin.7 Some skin of color patients present with petaloid seborrheic dermatitis—pink or hypopigmented polycyclic coalescing rings with minimal scale.7,8
• Discoid lupus erythematosus, similar to seborrheic dermatitis, might present as pruritic, scaly, hypopigmented patches. However, in the experience of the experts, a more common presentation is tender erythematous patches of hair loss with central hypopigmentation and surrounding hyperpigmentation.
Diagnostic clues for vertex and mid scalp alopecia include:
• Androgenetic alopecia typically presents as a reduction of terminal hair density in the vertex and mid scalp regions (with widening through the midline part) and fine hair along the anterior hairline.9 Signs of concomitant hyperandrogenism, including facial hirsutism, acne, and obesity, might be observed.10
• Central centrifugal cicatricial alopecia typically affects the vertex and mid scalp with a shiny scalp appearance and follicular dropout.
Diagnostic clues for frontotemporal alopecia include:
• Frontal fibrosing alopecia (FFA) often presents with spared single terminal hairs (lonely hair sign).