What is the differential diagnosis for hair loss in a 23‑year‑old male?

Differential Diagnosis of Hair Loss in a 23-Year-Old Male

In a 23-year-old male, androgenetic alopecia (male pattern hair loss) is the most likely diagnosis, followed by alopecia areata, telogen effluvium, and less commonly nutritional deficiencies, thyroid disease, or infectious causes. 1, 2

Primary Diagnostic Considerations

Androgenetic Alopecia (Most Common)

• Androgenetic alopecia affects up to 80% of males by age 80 and can begin in the early twenties, presenting with characteristic bitemporal recession of the frontal hairline followed by diffuse thinning at the vertex 3, 4, 5
• This condition results from sensitivity to dihydrotestosterone (DHT), causing progressive miniaturization of androgen-sensitive hair follicles 2, 6
• The affected scalp appears slightly reddened but otherwise normal, without inflammatory scaling 7
• Dermoscopy showing miniaturized hairs in a patterned distribution confirms the diagnosis 7

Alopecia Areata (Second Most Common in Young Adults)

• Alopecia areata is an autoimmune condition mediated by T lymphocytes attacking hair follicles, characterized by patchy, non-scarring hair loss 2
• Pathognomonic features include exclamation mark hairs (short broken hairs around expanding patches) and yellow dots on dermoscopy 2
• Approximately 20% have a family history, and the condition associates with other autoimmune diseases including thyroid disease, lupus, and vitiligo 2
• Nail changes (pitting, ridging, or dystrophy) occur in roughly 10% of patients and support the diagnosis 2

Telogen Effluvium

• Stress-induced shedding where physiologic or emotional stressors push hair follicles prematurely into the resting phase 2
• Triggers include illness, surgery, severe emotional stress, rapid weight loss, and nutritional deficiencies 2
• Dermoscopy lacks the yellow dots and exclamation mark hairs characteristic of alopecia areata 2

Less Common but Important Causes

Nutritional Deficiencies

• Iron deficiency is the most common nutritional deficiency worldwide and a sign of chronic diffuse telogen hair loss, with serum ferritin levels lower in patients with alopecia areata and androgenetic alopecia 2
• Vitamin D deficiency (<20 ng/mL) shows strong association with hair loss, with 70% of alopecia areata patients deficient versus 25% of controls 2
• Zinc deficiency impairs hair follicle function, with serum zinc levels tending to be lower in alopecia areata patients 2

Thyroid Disease

• Both hypothyroidism and hyperthyroidism can cause hair loss 1, 2
• TSH and free T4 should be checked to rule out thyroid dysfunction 2

Infectious Causes

• Tinea capitis (scalp ringworm) causes patchy hair loss with scalp inflammation and scaling, requiring fungal culture for diagnosis 2
• Signs may be subtle, making diagnosis challenging 2

Trichotillomania

• Compulsive hair pulling that mimics alopecia areata, distinguished by incomplete hair loss and firmly anchored broken hairs that remain in anagen phase 2

Systemic Diseases

• Systemic lupus erythematosus can cause both scarring and non-scarring alopecia 2
• Secondary syphilis presents with patchy "moth-eaten" hair loss 2

Diagnostic Algorithm

Clinical Examination

• Assess hair loss pattern: bitemporal recession with vertex thinning suggests androgenetic alopecia; patchy loss suggests alopecia areata; diffuse thinning suggests telogen effluvium 2
• Perform dermoscopy: look for miniaturized hairs (androgenetic alopecia), yellow dots and exclamation mark hairs (alopecia areata), or absence of these features (telogen effluvium) 2
• Examine for nail changes (pitting, ridging) which occur in 10% of alopecia areata patients 2
• Check for scalp inflammation or scaling suggesting tinea capitis 2

Laboratory Testing Strategy

For androgenetic alopecia with no signs of androgen excess: no routine laboratory testing is required 7

For alopecia areata with typical presentation: diagnosis is clinical; investigations are unnecessary in most cases 2

When diagnosis is uncertain or presentation is atypical, obtain targeted testing:

• Serum ferritin (iron deficiency) 2
• Vitamin D level (deficiency <20 ng/mL) 2
• Serum zinc level 2
• TSH and free T4 (thyroid disease) 2
• Fungal culture if inflammation or scaling present (tinea capitis) 2
• Scalp biopsy for difficult cases or when diagnosis remains uncertain 2

Only if signs of androgen excess are present (severe acne, hirsutism in unusual distribution):

• Free and total testosterone, DHEA-S, androstenedione 7

Common Pitfalls to Avoid

• Ordering excessive laboratory tests when the diagnosis is clinically evident – androgenetic alopecia and typical alopecia areata are diagnosed clinically 2
• Failing to consider the psychological impact, which may warrant assessment for anxiety and depression 2
• Overlooking dermoscopy as a non-invasive diagnostic tool that provides valuable diagnostic information 2
• Missing the natural history: 34-50% of alopecia areata patients recover within one year without treatment, making observation reasonable for limited disease 2

Prognostic Considerations

• Androgenetic alopecia is progressive and worsens over time; early treatment achieves the best outcome 3, 4
• Alopecia areata has variable prognosis: 34-50% recover within one year, but 14-25% progress to total scalp or body hair loss 2
• Childhood onset and ophiasis pattern (scalp margin involvement) carry poorer prognoses in alopecia areata 2