What causes loss of hair in one spot, also known as alopecia?

Hair Loss in One Spot (Alopecia Areata)

Primary Diagnosis

Hair loss in one spot is most commonly alopecia areata, an autoimmune condition where T lymphocytes attack hair follicles, causing patchy, non-scarring hair loss that typically appears as well-defined round or oval patches. 1

Key Diagnostic Features

Clinical Presentation:

• Smooth, round patches of complete hair loss without scalp scarring 1
• Exclamation mark hairs (short broken hairs with tapered bases) around expanding patches 1
• Can affect any hair-bearing area, though scalp is most common 1
• Approximately 20% of patients have a family history 1

Dermoscopy Findings (Trichoscopy):

• Yellow dots are the most common finding, present in 6-100% of patients and indicate active disease when regularly round 2
• Exclamation mark hairs help distinguish from other conditions like trichotillomania 2
• Black dots appear in 0-84% of cases 2

Differential Diagnoses to Rule Out

Other causes of focal hair loss include:

• Tinea capitis (scalp ringworm): presents with scalp inflammation, scaling, and requires fungal culture for diagnosis 1
• Trichotillomania (compulsive hair pulling): shows incomplete hair loss with firmly anchored broken hairs that remain in anagen phase, unlike the exclamation mark hairs of alopecia areata 1, 2
• Early scarring alopecia: requires skin biopsy for diagnosis 1
• Secondary syphilis: presents with patchy "moth-eaten" hair loss 1

Diagnostic Approach

Most cases do not require laboratory testing, as diagnosis is made clinically. 1

Laboratory testing is indicated when:

• Diagnosis is uncertain or presentation is atypical 1
• Diffuse alopecia areata is suspected (may require biopsy) 1
• Other systemic conditions need to be ruled out 1

Recommended tests when indicated:

• Fungal culture if tinea capitis suspected 1
• Skin biopsy for difficult cases or early scarring alopecia 1
• Vitamin D levels (70% of alopecia areata patients are deficient versus 25% of controls, with lower levels correlating inversely with disease severity) 1
• Serum zinc levels (tend to be lower in alopecia areata patients) 1
• TSH to rule out thyroid disease (alopecia areata associates with other autoimmune diseases including thyroid disease) 1
• Serology for lupus or syphilis if clinically suspected 1

Prognosis

Natural history varies significantly:

• 34-50% of patients recover within one year without treatment 1
• 14-25% progress to total scalp or body hair loss 1
• Patients with less than 25% hair loss initially have a 68% chance of being disease-free at follow-up, compared to only 8% for those with more than 50% initial hair loss 2
• Childhood onset and ophiasis pattern (scalp margin involvement) carry poorer prognoses 1

Treatment Options

For limited patchy alopecia areata:

• Intralesional corticosteroid injections (triamcinolone acetonide 5-10 mg/mL) are first-line treatment with the strongest evidence. 1, 3

For extensive patchy alopecia areata:

• Contact immunotherapy is the best-documented treatment, though response rates are lower in severe cases 1
• Oral prednisolone (starting at 40 mg daily with 6-week tapering course) may show >25% regrowth in 30-47% of patients 3

Nutritional supplementation:

• Vitamin D supplementation for patients with levels <20 ng/mL 1
• Zinc supplementation when deficient, particularly in resistant disease >6 months duration 1

Critical Pitfalls to Avoid

• Do not order excessive laboratory tests when diagnosis is clinically evident 1
• Do not overlook dermoscopy as a non-invasive diagnostic tool that provides valuable information and can guide biopsy site selection 1, 2
• Do not fail to assess for psychological impact, as alopecia areata may cause considerable anxiety and depression warranting formal assessment 1
• Remember that many cases are self-limited with spontaneous remission, making the tendency to spontaneous remission an important consideration before initiating aggressive treatment 1