En coup de sabre (ECS) is a rare, linear subtype of localized scleroderma, also known as morphea. The name is French for “strike of the saber,” which describes the lesion’s characteristic appearance: a depressed, linear groove most commonly occurring on the forehead and scalp. While generally confined to the face and scalp, ECS can affect underlying structures. It is more frequently observed in children and young adults, with a slight predominance in females.
Clinical Presentation and Affected Tissue Layers
The defining feature of ECS is a distinct, linear depression running vertically or diagonally across the frontoparietal region of the head. The lesion often begins as a slightly discolored streak—either hyperpigmented or hypopigmented—and may have a violaceous border during the active inflammatory phase. As the condition progresses, the streak becomes indurated and hardened, eventually evolving into a deeply atrophic, scar-like band with an ivory-like color. ECS usually first appears in the first two decades of life, with an average age of onset often cited in early adolescence.
The atrophy is not limited to the superficial skin layer. The process extends downward, sequentially affecting the subcutaneous fat layer, which is often severely diminished or entirely lost. In advanced cases, the destructive process can penetrate the underlying muscle, fascia, and even the periosteum of the skull. When the lesion extends into the scalp, it results in linear cicatricial alopecia, which is permanent hair loss due to scarring. Involvement of the underlying bone can lead to indentation or atrophy of the skull, contributing to a sunken appearance.
Underlying Causes and Autoimmune Link
The precise cause of en coup de sabre remains unknown, but it is widely considered an autoimmune inflammatory disease. This classification is based on histological findings of chronic inflammation and the condition’s responsiveness to immunosuppressive medications. The disease involves the overproduction and excessive deposition of collagen, leading to the characteristic thickening and hardening of the skin and adjacent tissues.
Early in the disease process, inflammatory pathways involving specific immune cells, such as CD4 helper T cells, are active, leading to perivascular lymphocytic infiltrates. Over time, this intense inflammatory state shifts toward a fibrotic phase, resulting in the dense, sclerotic tissue seen in the established lesion. While autoimmune dysfunction is the leading hypothesis, certain co-factors are suspected to act as triggers in genetically predisposed individuals. Environmental factors such as localized trauma to the head or face have been reported, suggesting a potential role for the Koebner phenomenon, where injury precipitates the disease. Furthermore, some studies have investigated a link to infections, though a definitive role for agents like Borrelia burgdorferi has not been conclusively established.
Diagnosis and Distinguishing Related Conditions
The diagnosis of ECS is primarily made through a thorough clinical examination, relying on the unique appearance and location of the linear, depressed lesion. The characteristic frontoparietal distribution and the presence of prominent cutaneous sclerosis are usually sufficient for a provisional diagnosis.
To confirm the diagnosis and assess the depth of tissue involvement, supportive tests are often utilized. A skin biopsy may be performed to reveal the histopathological signs of scleroderma, such as dense collagen bundles and a loss of skin appendages. Imaging studies, including magnetic resonance imaging (MRI) or computed tomography (CT) scans, are valuable for evaluating the extent of atrophy in deeper structures, like muscle, bone, and brain tissue, especially when neurological symptoms like seizures are present.
It is important to distinguish ECS from Parry-Romberg syndrome (PRS), a condition that causes progressive hemifacial atrophy. Both ECS and PRS are considered part of the spectrum of linear morphea and can sometimes coexist. PRS is characterized by slowly progressing atrophy that typically affects the lower half of the face and involves deeper structures like fat, muscle, and bone, often with minimal or absent cutaneous sclerosis. Conversely, ECS is defined by the prominent linear sclerotic plaque on the forehead and scalp. The distinction is medically important because ECS is a form of localized scleroderma, while PRS is often viewed as a more extensive form of progressive facial atrophy.
Treatment Approaches and Symptom Management
The primary goal of treatment for ECS is to halt the progression of the inflammatory and fibrotic process, particularly during the active phase. Medical management focuses on immunosuppression to prevent further tissue damage and atrophy.
The most common first-line systemic treatment is a combination of the disease-modifying anti-rheumatic drug methotrexate and oral corticosteroids. This combination therapy is often administered for an extended period, such as at least one year, and has shown efficacy in managing both cutaneous and potential extracutaneous involvement. For milder or superficial lesions, topical treatments such as corticosteroids, calcipotriene, or phototherapy (like UVA1) may be used to control localized inflammation.
Once the disease has entered a quiescent or “burnt-out” phase, treatment shifts toward aesthetic and functional correction of the residual deformity. Surgical interventions are aimed at addressing the volume loss and indentation caused by the atrophy. Reconstructive options include autologous fat grafting, where fat tissue is harvested from another part of the body and injected into the depressed area to restore volume. Dermal fillers, such as hyaluronic acid, can also be used for milder indentations. For more severe defects involving bone or deep tissue, complex procedures like synthetic implants, tissue expansion, or local tissue flaps may be required to achieve a satisfactory cosmetic outcome.