The clinical images provided demonstrate multiple well-demarcated, smooth patches of non-scarring hair loss on the scalp in different individuals. Which of the following is the most likely diagnosis?

Explanation

## Image Findings * Multiple, well-demarcated patches of hair loss on the scalp. * Smooth, completely bald areas within the patches. * Absence of scaling, erythema, or inflammation within the bald patches, indicating normal-appearing skin. * Non-scarring nature of the hair loss, meaning follicular units are preserved. * Patches vary in size and shape, observed in different individuals. ## Diagnosis **Key Point:** The presence of sudden onset, well-demarcated, smooth, non-scarring patches of complete hair loss on a normal-appearing scalp is pathognomonic for **Alopecia Areata**. Alopecia areata is an **autoimmune condition** characterized by the immune system mistakenly attacking the **anagen hair follicles**, leading to their premature entry into the telogen phase and subsequent shedding. The images clearly show **smooth, bald patches** without any signs of inflammation, scaling, or scarring, which are hallmark features. The **well-demarcated borders** further support this diagnosis, distinguishing it from diffuse or irregular patterns seen in other conditions. The non-scarring nature implies that the hair follicles are not permanently destroyed, allowing for potential regrowth. This contrasts with scarring alopecias where follicular destruction is irreversible. The varying sizes and shapes of the patches in different individuals highlight the diverse presentation of this condition. ## Differential Diagnosis | Feature | Correct Dx: Alopecia Areata | Alt 1: Tinea Capitis | Alt 2: Trichotillomania | | :------------------ | :--------------------------------------------------------- | :------------------------------------------------------------ | :----------------------------------------------------------- | | **Hair Loss Pattern** | Well-demarcated, smooth, round/oval patches of complete loss | Irregular patches with broken hairs (black dots), often scaling | Irregular patches with varying hair lengths (broken, stubble) | | **Scalp Appearance** | Normal, smooth, non-inflamed, non-scarring | Erythematous, scaly, inflamed; may have pustules or kerion | Normal or mild irritation; no inflammation/scaling | | **Hair Breakage** | Exclamation mark hairs at periphery | Broken hairs (black dots) within patches | Broken hairs of varying lengths, twisted, pulled | | **Associated Sx** | Often asymptomatic; may have nail pitting | Pruritus, lymphadenopathy; fungal infection | Psychological stress, anxiety, OCD; patient often denies pulling | | **Diagnosis** | Clinical; dermoscopy (exclamation mark hairs) | KOH mount, fungal culture | Clinical; dermoscopy (v-shaped hairs, broken hairs) | ## Clinical Relevance **Clinical Pearl:** Alopecia areata can affect any hair-bearing area, not just the scalp. It is often associated with other autoimmune conditions such as **thyroid disease (Hashimoto's, Graves'), vitiligo, and atopic dermatitis**. Screening for these comorbidities may be warranted, especially in extensive or recurrent cases. ## High-Yield for NEET PG **High-Yield:** **Exclamation mark hairs** (hairs that are narrower proximally and wider distally, resembling an exclamation mark) are a characteristic dermoscopic finding at the periphery of active alopecia areata patches. **Key Point:** Alopecia areata is a **T-cell mediated autoimmune disorder** targeting the anagen hair follicle. ## Common Traps **Warning:** Do not confuse the smooth, non-inflammatory patches of alopecia areata with the scaly, erythematous, and often pruritic patches of **tinea capitis**, which typically show broken hairs ("black dots") and require antifungal treatment. Similarly, differentiate from **trichotillomania** by the irregular, non-uniform hair lengths and the presence of broken, twisted hairs, often in accessible areas. ## Reference [cite:Bolognia, Jean L., et al. Dermatology. 4th ed., Elsevier, 2018.]