What is the appropriate evaluation and treatment for a patient presenting with a patch of hair missing from the scalp, potentially due to alopecia areata or other underlying autoimmune or skin disorders?

Evaluation and Treatment of Patchy Hair Loss from the Scalp

For a patient presenting with a patch of hair missing from the scalp, the most likely diagnosis is alopecia areata, which can typically be diagnosed clinically without laboratory testing by identifying characteristic features such as well-demarcated round patches, exclamation mark hairs at the periphery, and yellow dots on dermoscopy. 1

Clinical Diagnosis

Perform dermoscopy first as it is the single most useful non-invasive tool to confirm alopecia areata and differentiate it from other conditions 2. Look specifically for:

• Yellow dots (regularly round, present in 6-100% of cases, indicating active disease) 1, 2
• Exclamation mark hairs (short broken hairs at the periphery, pathognomonic for alopecia areata) 1, 2
• Black dots (present in 0-84% of cases) 2
• Cadaverized hairs (indicating active disease) 1

Clinical examination should identify:

• Well-demarcated round or oval patches of complete hair loss with normal-appearing skin and preserved follicular openings 1
• Positive hair pull test at the margins of expanding patches (signals active disease) 1
• Nail changes such as pitting, ridging, or dystrophy (occur in approximately 10% of patients) 1

When Laboratory Testing is NOT Needed

In most cases of alopecia areata, investigations are unnecessary as the diagnosis is made clinically 1. Avoid ordering excessive laboratory tests when characteristic dermoscopic features (yellow dots and exclamation mark hairs) are clearly present 1.

When Laboratory Testing IS Indicated

Order targeted laboratory tests only when:

• Diagnosis is uncertain or presentation is atypical 1
• Diffuse alopecia areata is suspected (may require histopathologic confirmation) 1
• Other conditions need to be excluded from the differential diagnosis 1

Recommended laboratory panel when testing is indicated:

• Serum ferritin (check for iron deficiency, most common nutritional deficiency worldwide) 1
• TSH (rule out thyroid disease, a common cause of hair loss) 1
• Vitamin D level (70% of alopecia areata patients are deficient versus 25% of controls, with lower levels correlating inversely with disease severity) 1
• Serum zinc (tends to be lower in alopecia areata patients, particularly those with resistant disease >6 months) 1
• Fungal culture (mandatory if tinea capitis is suspected) 1
• Skin biopsy (for difficult cases, early scarring alopecia, or when diagnosis remains uncertain after dermoscopy) 1

Differential Diagnosis to Exclude

Trichotillomania can mimic alopecia areata but is distinguished by:

• Incomplete hair loss rather than well-demarcated patches 1
• Broken hairs that remain firmly anchored in the scalp (unlike exclamation mark hairs) 2

Tinea capitis presents with:

• Scalp inflammation and scaling 1
• Requires fungal culture for definitive diagnosis and oral antifungal treatment 1

Other conditions to consider: telogen effluvium, early scarring alopecia, systemic lupus erythematosus, and secondary syphilis 1

Treatment Algorithm

For limited patchy alopecia areata (<25% scalp involvement):

• Intralesional corticosteroid injections are first-line treatment with the strongest evidence (Strength of recommendation B, Quality of evidence III) 1
• Alternatively, topical corticosteroids (such as 0.1% triamcinolone acetonide cream twice daily) can be used 3
• Observation is reasonable as 34-50% of patients recover within one year without treatment 1

For extensive patchy alopecia areata (>25% scalp involvement):

• Contact immunotherapy is the best-documented treatment, though response rates are lower in severe cases 1

Adjunctive micronutrient supplementation:

• Vitamin D supplementation for patients with levels <20 ng/mL (<50 nmol/L), following general international recommendations for adults 1
• Zinc supplementation when deficient, particularly in resistant cases 1
• Iron supplementation if ferritin is low 1

Topical minoxidil 5% can be used as adjunctive therapy, though it is FDA-approved specifically for androgenetic alopecia in men, not alopecia areata 4

Prognostic Factors

Disease severity at presentation is the strongest predictor of long-term outcome 2:

• Patients with <25% hair loss initially have a 68% chance of being disease-free at follow-up 2
• Patients with >50% initial hair loss have only an 8% chance of being disease-free 2
• Childhood onset and ophiasis pattern (scalp margin involvement) carry poorer prognoses 1
• 14-25% of patients progress to total scalp or body hair loss 1

Common Pitfalls to Avoid

• Do not order excessive laboratory tests when the diagnosis is clinically evident with characteristic dermoscopic findings 1
• Do not overlook the psychological impact of alopecia areata, which may cause considerable psychological and social disability warranting assessment for anxiety and depression 1
• Do not forget to screen for associated autoimmune diseases including thyroid disease (check TSH), diabetes mellitus (check fasting glucose), lupus, and vitiligo, as approximately 20% of patients have a family history and the condition associates with other autoimmune disorders 1, 3
• Do not miss the tendency toward spontaneous remission when counseling patients, as many cases are self-limited 1