The buttonhole sign is a bedside clinical test in which a skin lesion can be pushed inward through the surrounding tissue with gentle finger pressure, briefly disappearing or inverting into a small pit before popping back out. It gets its name from the way a button slips through a fabric hole: the soft, pliable mass passes through a ring of dermis when pressed. The sign is most closely associated with neurofibromas, though it also appears in a handful of other conditions where the skin or underlying connective tissue has lost its normal firmness. Because it requires nothing more than a fingertip and a few seconds, the maneuver remains one of the quickest and most reliable clues a clinician can use to narrow a differential diagnosis at the bedside.
How the Maneuver Is Performed
The test itself is remarkably simple. The examiner places the pad of one finger directly over the lesion and applies steady, gentle downward pressure. In a positive result, the nodule or papule gives way and sinks inward through a defect or zone of laxity in the dermis, sometimes disappearing entirely beneath the skin surface. When pressure is released, the lesion slowly herniates back outward and resumes its original shape. The whole sequence takes only a few seconds.
What makes a positive result meaningful is the quality of the invagination. Many soft-tissue bumps will flatten if you push hard enough, but a truly positive buttonhole sign involves the lesion slipping through a discrete opening rather than simply compressing in place. The feeling under the fingertip is distinctive: there is a brief moment of resistance, then a sudden give as the mass passes through. Clinicians sometimes describe it as feeling like pushing a marble through a tight ring. That snap-through quality, rather than gradual squishing, is what separates a true positive from ordinary softness.
Neurofibromas and the Classic Context
The buttonhole sign is most famously associated with neurofibromas, the benign nerve-sheath tumors that arise in neurofibromatosis type 1 (NF1). Cutaneous neurofibromas sit within the dermis or just beneath it, and they are composed of a loose, gelatinous mix of Schwann cells, fibroblasts, mast cells, and collagen. That soft, almost rubbery internal architecture is what allows them to be invaginated so easily. Most other firm skin nodules, such as cysts or lipomas, lack this particular combination of pliability and attachment to the surrounding dermis, so they either compress in place or slide away from the finger rather than passing through.
In a patient with multiple cutaneous neurofibromas, performing the buttonhole sign on several lesions can help confirm the clinical impression quickly, especially when other NF1 features such as café-au-lait macules, axillary freckling, or Lisch nodules are present. While no single physical sign is enough to diagnose NF1 on its own, the buttonhole sign is one of the most recognizable bedside findings and often the one that prompts a new referral for genetic evaluation when a patient presents with multiple soft bumps of uncertain origin.
Solitary neurofibromas also occur in people without NF1, and the buttonhole sign works equally well on those. A single soft nodule on the trunk or limbs that invaginates on pressure is strongly suggestive of a neurofibroma, and this finding alone may spare the patient an unnecessary biopsy when the clinical picture is otherwise reassuring.
Why Soft Tissue Architecture Matters
The buttonhole sign works because the lesion and the tissue around it differ in mechanical stiffness. The neurofibroma (or other soft mass) is more compliant than the surrounding dermis, and there is a natural opening or zone of weakness in the connective tissue through which the mass can be displaced. Think of it like a hernia on a miniature scale: the contents are softer than the wall, and there is a gap through which they can be pushed.
In healthy skin, elastic fibers and collagen form a taut meshwork that resists invagination. When that meshwork is intact, pressing on a bump simply flattens it. But when the lesion itself is unusually soft, or when the elastic tissue around it has been weakened or destroyed, the mass can slip through. This is why the sign also appears in conditions defined by elastic-fiber loss, not just in nerve-sheath tumors.
Anetoderma and Elastic Fiber Loss
Anetoderma is a much less common condition in which localized patches of skin lose their elastic fibers, leaving behind areas that feel slack and hernia-like. A case report of Schweninger-Buzzi type anetoderma described a solitary, skin-colored papule with a sac-like herniation that demonstrated a characteristic buttonhole sign on palpation.1PubMed Central. Schweninger-Buzzi anetoderma with rare facial presentation: a case report The mechanism here is different from that in neurofibromas. Instead of a soft tumor slipping through firm skin, the skin itself has become so lax from elastic-fiber destruction that the tissue can be pushed inward like a deflated balloon.
Histopathological studies of anetoderma confirm the underlying cause: focal loss of normal elastic fibers is the defining feature, found in all cases in one series of 15 patients. Those same specimens showed a perivascular infiltrate of lymphocytes, suggesting that the elastic-fiber destruction is driven by inflammation rather than by a simple structural defect.2JAMA Dermatology. Histopathologic Findings in Anetoderma In clinical practice, when a buttonhole sign is positive but the overlying skin looks atrophic or slack rather than nodular, anetoderma moves up the list of possibilities. The lesions tend to appear as small outpouchings on the trunk or upper arms, and they can be primary (arising in previously normal skin) or secondary (developing at sites of prior inflammation, such as resolved acne or varicella).
The clinical feel of anetoderma is subtly different from that of a neurofibroma. With a neurofibroma, you feel a discrete mass slipping through a hole. With anetoderma, the skin itself collapses inward without much resistance, more like poking a finger into a loosely filled pouch. Both produce a positive buttonhole sign, but the quality of the invagination can help a clinician tell them apart before any biopsy is done.
The Dimple Sign in Dermatofibromas
A related but distinct bedside maneuver is the dimple sign, which is most strongly associated with dermatofibromas. Dermatofibromas are common, benign, pigmented papules or nodules that are usually found on the legs and produce a characteristic dimpling when laterally squeezed.3PubMed Central. Multiple dermatofibromas: dermoscopic patterns The maneuver is different from the buttonhole test: instead of pressing straight down, the clinician pinches the skin on either side of the lesion between thumb and forefinger. A dermatofibroma is tethered to the overlying epidermis, so lateral compression causes the center to pucker inward, creating a small dimple.
Some texts refer to this dimple sign as a “buttonhole sign,” and the two terms are occasionally used interchangeably in older literature. This overlap causes real confusion, so it is worth keeping the distinction clear. The classic buttonhole sign involves axial pressure pushing a mass through the dermis, while the dimple sign involves lateral compression producing surface puckering. A dermatofibroma will dimple when squeezed from the sides but will not invaginate when pressed straight down, because the lesion is firm and fibrotic rather than soft and gelatinous. A neurofibroma will invaginate when pressed directly but generally will not dimple with lateral compression, because it is not tethered to the epidermis the way a dermatofibroma is.
This distinction matters practically. Dermatofibromas and neurofibromas can look similar on casual inspection: both present as small, dome-shaped, skin-colored to brownish nodules. The two signs point in opposite diagnostic directions, so performing both maneuvers takes seconds and can prevent a misdiagnosis.
When the Buttonhole Sign Is Negative but Expected
Not every neurofibroma produces a convincing buttonhole sign. Plexiform neurofibromas, which grow along the length of a nerve and involve deeper tissue planes, tend to feel ropy or bag-like rather than discrete, and they may not invaginate neatly. Very small cutaneous neurofibromas may not have enough bulk to demonstrate the sign convincingly, and fibrotic or long-standing lesions can become stiff enough to resist invagination. A negative result does not rule out a neurofibroma; it just means the bedside test has reached its limits and imaging or biopsy may be needed.
Similarly, early anetoderma may present as subtle areas of skin laxity that are not yet pronounced enough to produce a clear positive result. The buttonhole sign is most reliable when the condition is well established and the lesion is of a size the finger can isolate. In ambiguous cases, dermoscopy and ultrasound imaging have become useful adjuncts, though neither has fully replaced the time-honored finger-pressure test for an initial clinical impression.
The Boutonnière Deformity and the French Connection
The word “boutonnière” is French for “buttonhole,” and in hand surgery it names a specific finger deformity that has nothing to do with skin invagination. A boutonnière deformity occurs when the central slip of the extensor tendon over the proximal interphalangeal (PIP) joint is disrupted, allowing the lateral bands of the tendon to slip to either side. The PIP joint then flexes while the fingertip hyperextends, producing a characteristic zigzag posture. The name comes from the anatomical image: the head of the proximal phalanx pokes through the torn tendon like a button through a buttonhole.
Though the boutonnière deformity shares linguistic roots with the dermatological buttonhole sign, the two are entirely separate clinical entities examined in entirely different specialties. The deformity is managed surgically when conservative splinting fails. One case report described a patient with chronic post-traumatic boutonnière deformity who regained full flexion and extension of the affected finger after reconstruction involving release of the central slip and lateral bands, tendon reconstruction, and fixation with a wire, with satisfactory alignment and function at one year follow-up.4PubMed Central. Posttraumatic chronic boutonniere deformity correction using ala carte reconstruction and local anesthesia surgery, A case report
The shared etymology occasionally trips up students encountering both terms for the first time, and it is worth emphasizing that a “positive buttonhole sign” on a dermatology exam has no relationship to a boutonnière deformity on an orthopedic exam. Context always disambiguates, but awareness of the overlap saves some initial bewilderment.
Other Conditions That Can Mimic the Sign
A few other soft-tissue lesions can produce something that resembles the buttonhole sign, even though they are not the classic teaching examples. Lipomas that sit within a fascial defect may slip through the opening under pressure, mimicking the snap-through feel. Some epidermal cysts in areas of lax skin will depress easily. Even certain vascular malformations that are highly compressible can partially empty under finger pressure and refill when released, simulating invagination.
The key clinical differentiator is what happens after you let go. A neurofibroma herniates back out slowly and resumes its original dome shape. A lipoma sliding through a fascial defect may or may not return to its original position, and it often feels lobulated rather than smooth. A vascular lesion refills with blood and often has a bluish hue that blanches under pressure. These subtle differences in texture, color, and recovery time help the experienced examiner sort through the possibilities without reaching for a scalpel.
Where Imaging Fits In
Ultrasound and MRI have expanded the toolkit for evaluating lesions that produce a positive buttonhole sign, but they serve complementary rather than competing roles. High-frequency ultrasound can reveal the internal echogenicity and depth of a soft-tissue nodule in real time, which is helpful when the clinical picture is ambiguous. A hypoechoic, well-circumscribed lesion in the dermis that is compressible under the transducer probe is consistent with a neurofibroma. MRI is more informative for plexiform neurofibromas, where the extent of nerve involvement matters for surgical planning.
For anetoderma, imaging is less commonly needed because the clinical presentation and a skin biopsy showing elastic-fiber loss are usually sufficient. However, ultrasound can occasionally reveal the thinned dermis and confirm the hernia-like quality of the lesion in cases where the clinical picture is subtle. In practice, the buttonhole sign remains a first-pass screening tool; imaging and biopsy come in when the sign alone cannot resolve the diagnosis or when the clinician needs to characterize the lesion in more detail before deciding on management.
Teaching Value and Bedside Examination Culture
The buttonhole sign occupies an interesting niche in medical education. It belongs to a broader tradition of eponymous clinical signs in dermatology, many of which date to an era when bedside examination was the primary diagnostic technology. Signs like the Auspitz sign in psoriasis, the Nikolsky sign in blistering diseases, and the dimple sign in dermatofibromas all share the same philosophy: a simple physical maneuver that gives immediate diagnostic information without any equipment.
In an era of dermoscopy, high-resolution ultrasound, and rapid-access biopsy, some educators worry that these hands-on skills are being lost. The buttonhole sign is a case in point. It takes a few seconds, costs nothing, and provides a finding that no imaging study replicates exactly, because the quality of the invagination is a tactile experience that can only be appreciated with a fingertip. A radiologist can tell you a lesion is hypoechoic and compressible, but the snap-through feel of a positive buttonhole sign is something you have to perform yourself to appreciate fully. For that reason, it continues to be taught in dermatology and general practice clerkships as an example of what physical examination can accomplish when done attentively.