What is the differential diagnosis and management for an 18-year-old female presenting with hair loss?

Differential Diagnosis of Hair Loss in an 18-Year-Old Female

The most common causes of hair loss in an 18-year-old female are telogen effluvium (stress-induced shedding), alopecia areata (autoimmune patchy hair loss), androgenetic alopecia (pattern hair loss), nutritional deficiencies (particularly iron, vitamin D, and zinc), and thyroid disease. 1

Primary Differential Diagnoses

Autoimmune Causes

• Alopecia areata presents as patchy, non-scarring hair loss with characteristic exclamation mark hairs (short broken hairs) around expanding patches, mediated by T lymphocytes attacking hair follicles 1
• Approximately 20% have a family history, and it associates with other autoimmune diseases including thyroid disease, lupus, and vitiligo 1
• Dermoscopy reveals yellow dots, exclamation mark hairs, and cadaverized hairs 1
• Prognosis varies: 34-50% recover within one year spontaneously, but 14-25% progress to total scalp or body hair loss 1

Stress-Related Hair Loss

• Telogen effluvium is stress-induced shedding where physiologic or emotional stressors (illness, surgery, rapid weight loss, severe emotional stress) push hair follicles prematurely into the resting phase 1
• This is often self-limited, with spontaneous remission in up to 80% of cases with short duration (<1 year) once the triggering cause is eliminated 2
• Presents as diffuse hair thinning rather than patchy loss 3

Hormonal/Pattern Hair Loss

• Androgenetic alopecia (female pattern hair loss) is the most common cause of hair loss in women, beginning between ages 12-40 years 3, 4
• Presents with diffuse thinning over the frontal/parietal scalp with intact frontal hairline, sparing the occipital scalp 5, 4
• Most women have normal menses and pregnancies; extensive hormonal testing is unnecessary unless signs of androgen excess are present (hirsutism, severe cystic acne, virilization, irregular periods) 4

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 women with hair loss 1
• Vitamin D deficiency (<20 ng/mL) shows strong association with hair loss, with 70% of alopecia areata patients deficient versus 25% of controls, and lower levels correlate inversely with disease severity 1
• Zinc deficiency impairs hair follicle function, with serum zinc levels tending to be lower in alopecia areata patients 1

Infectious Causes

• Tinea capitis (scalp ringworm) causes patchy hair loss with scalp inflammation and scaling, requires fungal culture for diagnosis 1
• Signs may be subtle, making diagnosis challenging 1

Physical/Mechanical Causes

• Trichotillomania (compulsive hair pulling) mimics alopecia areata but is distinguished by incomplete hair loss and firmly anchored broken hairs that remain in anagen phase 1

Systemic Disease-Related

• Thyroid disease (both hypo- and hyperthyroidism) can cause diffuse hair loss 1
• Systemic lupus erythematosus can cause both scarring and non-scarring alopecia 1
• Secondary syphilis presents with patchy "moth-eaten" hair loss 1

Diagnostic Approach

Clinical Evaluation

• Determine the pattern: diffuse versus patchy, scarring versus non-scarring 3
• Look for exclamation mark hairs (alopecia areata), scalp inflammation/scaling (tinea capitis), or intact frontal hairline with vertex thinning (androgenetic alopecia) 1, 4
• Assess for signs of androgen excess: acne, hirsutism, irregular periods 4
• Identify potential triggers: recent stress, illness, surgery, rapid weight loss, medications 1

First-Line Laboratory Testing

For diffuse hair loss without obvious patchy alopecia or scalp lesions, obtain: 6

• Serum ferritin (iron deficiency if <60 ng/mL) 6
• TSH to rule out thyroid disease; if abnormal, add free T4 and thyroid peroxidase (TPO) antibodies 1, 6
• Vitamin D level (deficiency defined as <20 ng/mL) 1, 6
• Serum zinc level 1, 6
• Complete blood count 6

Additional Testing When Indicated

• If signs of androgen excess are present: total or free/bioavailable testosterone, sex hormone binding globulin (SHBG), screen for polycystic ovary syndrome (PCOS), prolactin level if hyperprolactinemia suspected 6
• If tinea capitis suspected: fungal culture 1
• If diagnosis uncertain or atypical presentation: skin biopsy, particularly for early scarring alopecia or diffuse alopecia areata 1
• If systemic lupus suspected: serology for lupus erythematosus 1
• If secondary syphilis suspected: syphilis serology 1

When Laboratory Testing is Unnecessary

• Most cases of alopecia areata are diagnosed clinically without laboratory workup 1
• Avoid ordering excessive laboratory tests when the diagnosis is clinically evident 1

Management Approach

Alopecia Areata

• For limited patchy hair loss: intralesional corticosteroid (triamcinolone acetonide 5-10 mg/mL) is first-line treatment with strongest evidence 7, 2
• For extensive patchy hair loss: contact immunotherapy is the best-documented treatment, though response rates are lower in severe cases 7
• Many cases are self-limited with 34-50% recovering within one year without treatment 1

Telogen Effluvium

• Address and eliminate the underlying trigger (stress, nutritional deficiency, illness) 1
• Spontaneous remission occurs in up to 80% of cases with short duration (<1 year) 2
• Nutritional supplementation if deficiencies identified 2

Androgenetic Alopecia

• Topical minoxidil 2-5% twice daily is first-line treatment and the only FDA-approved topical treatment for women 5, 3, 4
• If associated with high androgen levels, systemic antiandrogen therapy may be needed 5

Nutritional Deficiencies

• Vitamin D supplementation for levels <20 ng/mL 1
• Iron supplementation for ferritin <60 ng/mL, with reassessment at 3 months 6
• Zinc supplementation when deficient 1

Tinea Capitis

• Requires oral antifungal therapy (topical treatment is insufficient) 1

Common Pitfalls to Avoid

• Failing to consider the psychological impact: Hair loss may cause considerable psychological and social disability warranting assessment for anxiety and depression 1
• Over-testing clinically evident cases: Alopecia areata is typically diagnosed clinically; avoid excessive laboratory tests when diagnosis is clear 1
• Overlooking dermoscopy: This non-invasive diagnostic tool provides valuable information (yellow dots, exclamation mark hairs) 1
• Missing the self-limited nature: Many cases of alopecia areata and telogen effluvium resolve spontaneously, making watchful waiting appropriate in many cases 1, 2
• Inadequate hormonal workup when indicated: In women with signs of androgen excess (hirsutism, severe acne, irregular periods), hormonal testing is essential 6, 4