A sudden linear forehead depression resembling a lightning-shaped scar

This de-identified 2026 clinical story concerns a sudden linear depression on one side of the forehead.

Linear scleroderma en coup de sabre and progressive hemifacial atrophy were considered first, while TMJ function and craniofacial muscle tension were observed as additional findings.

A new linear forehead depression should not be explained as a TMJ problem first. Persistent or progressive change requires dermatologic evaluation, with neurologic or ophthalmic assessment when indicated, before jaw and muscle function are considered.

A soft intraoral appliance was used after coexisting functional findings were assessed. The line was no longer clearly visible the next day, but this temporal sequence does not establish that the appliance reversed the depression.

Observed timeline

The patient presented soon after the linear depression appeared. TMJ and craniofacial-muscle function were assessed, a soft intraoral appliance was used, and the next day the same linear depression was not visibly evident. Observation continues for recurrence or other change.

Before-and-next-day photographs were not standardized for distance, angle, lighting, expression, hydration, or hair position. They cannot quantify soft-tissue depth or volume, and the identifiable full face is not published.

A 'Harry Potter scar' noticed in the mirror

The patient said, “I woke up, looked in the mirror, and the upper left forehead was deeply indented like a Harry Potter scar.”

People around the patient wondered about sleeping with a hand or arm under the forehead or pressure from a watch. Temporary sleep-pressure marks are common, but this line persisted longer and felt different from the patient's usual marks, so simple pressure could not be assumed.

Two important differential diagnoses

A sword-cut-like linear depression on one side of the forehead is unusual. Appearance and photographs alone cannot diagnose it, but clinicians consider en coup de sabre and Parry-Romberg syndrome.

1. Linear scleroderma en coup de sabre

This form of localized scleroderma may produce a linear indurated depression on the forehead or scalp, with pigment change or scarring alopecia. Subcutaneous tissue, muscle, and rarely deeper structures can be involved, and neurologic manifestations have been reported.

2. Parry-Romberg syndrome

Progressive hemifacial atrophy is a rare disorder in which skin, subcutaneous fat, muscle, and sometimes deeper tissues on one side of the face gradually atrophy. Clinical overlap with en coup de sabre has been reported.

Typical findings not evident at this examination

No clear progressive skin sclerosis or induration, marked pigment change, scalp hair loss, or gradual atrophy of an entire facial side was observed at that time.

This difference from typical presentations was a useful clue but did not completely exclude either disease. Early lesions may be subtle; persistence, progression, or new change warrants dermatologic follow-up.

TMJ and craniofacial muscle assessment

While priority medical diagnoses and warning signs were considered, the examination also found TMJ functional disturbance and prominent tension in the temporalis, frontalis, and other masticatory or craniofacial muscles.

This did not diagnose the forehead depression as TMD. It identified a coexisting functional issue.

Assessment may include opening range and path, joint sound, catching and pain, muscle tension and familiar-pain reproduction, clenching or grinding, sleep and fatigue, and contour change over time or posture.

Treatment targeted the confirmed functional problem, not the forehead depression

The goal was conservative reduction of the observed TMJ dysfunction and craniofacial muscle hypertonicity, not direct removal of the forehead line.

A relatively flexible soft intraoral appliance was chosen for this individual muscle-dominant presentation. It is not a standard treatment for linear forehead depression and is not claimed to be superior to a conventional stabilization appliance.

The depression was not visible the following day and observation continues for recurrence, pigment or firmness change, alopecia, facial asymmetry, or neurologic symptoms.

Temporal association is not causation

The next-day change is worth recording, but natural recovery, lighting, expression, camera angle, hydration, and other factors were not excluded. It cannot be stated that the appliance restored the forehead contour.

Clinical hypothesis about muscle and fascial tension

The frontalis, temporalis, and surrounding craniofacial fascia are anatomically continuous.

One clinical question was whether directional tension could transiently alter superficial soft-tissue contour even without primary skin disease, making the underlying frontal bone easier to palpate.

There was no before-and-after ultrasound, MRI, elastography, or histology to support this mechanism. It remains an unverified hypothesis from one case, not an established pathophysiology or claim of a first report.

Clinical questions raised by the case

First, evaluation of a linear forehead depression must avoid missing rare skin disease and neurologic involvement. Second, craniofacial muscle function may be examined when typical rare-disease findings are not evident.

Third, contour change around treatment is an observation requiring research, not a new diagnostic criterion or therapy.

Limitations

This was one patient. Causality between TMJ dysfunction and the depression cannot be established. Soft-tissue change was not quantified with ultrasound, MRI, elastography, or biopsy.

The photographs were not a standardized research series with identical lighting, expression, and distance. Similar cases would require standardized photography and objective soft-tissue imaging and muscle-fascial assessment.

Changes requiring dermatology or neurology first

Priority evaluation is needed if the depression rapidly deepens or spreads; skin becomes firm or red, purple, or brown; scalp alopecia or progressive hemifacial atrophy appears; or new severe headache, seizure, weakness, sensory change, slurred speech, vision loss, field change, double vision, or severe eye pain occurs.

In these situations, dermatology-led evaluation with neurologic or ophthalmic assessment should precede TMJ observation. Even without warning signs, persistent or recurrent depression should not be self-diagnosed from photographs.

Research cited with this case

Tollefson MM, Witman PM. En coup de sabre morphea and Parry-Romberg syndrome: a retrospective review of 54 patients. J Am Acad Dermatol. 2007;56(2):257–263. DOI: 10.1016/j.jaad.2006.10.959.

Papara C, et al. Morphea: The 2023 update. Front Med (Lausanne). 2023;10:1108623. DOI: 10.3389/fmed.2023.1108623.

Tolkachjov SN, Patel NG, Tollefson MM. Progressive hemifacial atrophy: a review. Orphanet J Rare Dis. 2015;10:39. DOI: 10.1186/s13023-015-0250-9.

Careta MF, Romiti R. Localized scleroderma: clinical spectrum and therapeutic update. An Bras Dermatol. 2015;90(1):62–73. DOI: 10.1590/abd1806-4841.20152890.

These sources informed the clinical features, overlap, and evaluation of en coup de sabre and Parry-Romberg syndrome. They do not support the hypothesis that this patient's depression was caused by TMJ dysfunction or muscle tension.

Frequently asked questions

Is a sudden line on the forehead just a sleep-pressure mark?

Temporary pressure marks are common and usually fade relatively quickly. Persistence, deepening, skin color or firmness change, scalp change, or facial contour change warrants dermatologic evaluation and standardized photographs over time.

Can TMJ dysfunction cause a linear forehead depression?

Current evidence does not support that claim. This case recorded a temporal change after appliance use, but natural recovery and measurement conditions were not excluded.

How do en coup de sabre and Parry-Romberg syndrome differ?

En coup de sabre is a form of localized scleroderma characterized by a linear, depressed, and hardened lesion on the forehead or scalp.

Parry-Romberg syndrome usually presents as slowly progressive atrophy of the skin, subcutaneous tissue, muscle, and sometimes deeper structures on one side of the face.

Their features can overlap, so photographs alone cannot distinguish them and dermatologic assessment is required.

Does absence of sclerosis or alopecia exclude rare disease?

No. Their absence is useful but one examination cannot completely exclude an early lesion. Persistent or progressive change requires dermatologic follow-up.

Which accompanying symptoms require more urgent evaluation?

Dermatologic evaluation is needed if the depression rapidly deepens or widens, the skin becomes firm or changes color, scalp hair loss appears, or one side of the face progressively atrophies.

New severe headache, seizure, weakness, sensory change, slurred speech, vision or visual-field change, double vision, or severe eye pain requires neurologic, ophthalmologic, or emergency evaluation first.

Is a soft oral appliance a treatment for this depression?

No. It was selected to manage separately observed jaw function and muscle tension. The next-day visual change does not make it a standard treatment or establish superiority over other appliances.