What is the best evidence-based protocol for differentiating between linear morphea and lichen sclerosus (LS) in a 19-year-old female patient with a slightly hypopigmented patch surrounded by hyperpigmented patches in a linear pattern on the forehead, associated with atrophy and alopecia of the eyebrows?

Differentiating Linear Morphea from Lichen Sclerosus on the Forehead

The best evidence-based protocol for differentiating between linear morphea and lichen sclerosus in this case requires a skin biopsy from the most active sclerotic area of the forehead lesion, as histopathological examination is essential when diagnostic uncertainty exists or when lesions have atypical features. 1

Clinical Features to Consider in Differentiation

• Linear morphea typically presents with sclerotic, indurated plaques in a linear distribution, while lichen sclerosus (LS) presents with porcelain-white papules and plaques, often with areas of ecchymosis 1
• The presence of atrophy without hardening or sclerotic changes is more consistent with lichen sclerosus, as morphea typically shows induration and sclerosis 2
• Eyebrow alopecia can occur in both conditions but is more commonly reported with lichen sclerosus affecting the face 3
• Extragenital LS can present on the face and scalp in a linear pattern that may mimic "en coup de sabre" seen in linear morphea 3
• Hypopigmented patches surrounded by hyperpigmentation can occur in both conditions but is a common presentation in extragenital LS 1

Diagnostic Protocol

1. Skin Biopsy (Gold Standard):

   • Take the biopsy from the most active sclerotic area 1
   • Histopathological features to differentiate:
     • LS: Epidermal atrophy, hydropic degeneration of basal cells, homogenization of collagen in upper dermis, and significant loss of elastic fibers 4, 5
     • Morphea: Thickened epidermis, dense collagen bundles throughout dermis, and relative preservation of elastic fibers 4, 5

2. Specialized Histological Staining:

   • Picrosirius red staining under polarized light:
     • In morphea: Collagen fibers appear green in papillary and reticular dermis, except immediately below epidermis (orange-yellow) 4
     • In LS: Collagen fibers appear green in reticular dermis, with orange to greenish-orange fibers in papillary dermis 4
   • Toluidine blue staining for acid glycosaminoglycans shows different birefringence patterns 4

3. Advanced Imaging Techniques:

   • Multiphoton microscopy (MPM) can differentiate between the conditions by quantifying:
     • Increased collagen fibers in morphea compared to LS 5
     • Significant diminution of elastic fibers in the dermis of LS 5

4. Clinical Assessment Tools:

   • For suspected morphea, use the Localized Scleroderma Cutaneous Assessment Tool (LoSCAT) to evaluate disease activity and damage 2
   • Examine for other sites of involvement, particularly genital LS, as 45% of patients with plaque morphea have associated genital LS 6

Important Differentiating Features

• Epidermal changes: Epidermis is typically thick in morphea and thin in lichen sclerosus 4
• Elastic fiber distribution: Significant loss of elastic fibers in LS compared to morphea 5
• Collagen arrangement: Different patterns of collagen organization and birefringence 4
• Associated conditions: Check for genital involvement, as patients with morphea have a significantly higher frequency of genital LS (38% vs 3% in controls) 6

Pitfalls and Caveats

• Linear extragenital LS can clinically mimic linear morphea (en coup de sabre), leading to misdiagnosis if relying solely on clinical appearance 3
• Some cases may represent overlap syndromes sharing features of both conditions, making histopathological confirmation essential 1
• Early lesions of both conditions may show inflammatory changes that can confound diagnosis, so biopsy from the most active area is crucial 1
• The presence of alopecia in this case favors LS but is not definitive, as both conditions can affect hair follicles 3

In this specific case of a 19-year-old female with a hypopigmented patch surrounded by hyperpigmented patches in a linear pattern on the forehead with atrophy and eyebrow alopecia but without hardening or sclerotic changes, the presentation is more consistent with extragenital lichen sclerosus, but a biopsy is essential for definitive diagnosis 1, 3.