Molluscoid pseudotumors are soft, fleshy nodules that form on the skin, most commonly associated with Ehlers-Danlos syndrome (EDS), a group of inherited disorders affecting connective tissue. They develop at sites of repeated trauma or scarring, where abnormal connective tissue accumulates beneath the skin surface. Despite the alarming name, they are not true tumors and do not carry a risk of malignancy. Their clinical significance lies mainly in what they signal about the underlying connective-tissue disorder and the diagnostic confusion they can cause when other conditions produce similar-looking skin lesions.
How Molluscoid Pseudotumors Form
In people with classical Ehlers-Danlos syndrome, the skin and underlying connective tissue are unusually fragile. Minor injuries that would heal uneventfully in most people can trigger an exaggerated repair response. When the skin is damaged, blood pools beneath it to form small hematomas, and the body lays down scar tissue in an attempt to repair the site. In EDS, this repair process goes awry. Instead of producing normal scar tissue, the body deposits disorganized connective tissue that accumulates into a palpable nodule. These nodules are the molluscoid pseudotumors, and they tend to appear at pressure points and areas prone to repeated minor trauma, particularly the elbows, knees, and shins.1ResearchGate. Histopathological characterisation of molluscoid pseudotumour seen in Ehlers–Danlos syndrome
The underlying problem is a defect in collagen, the structural protein that gives skin, tendons, and blood vessels their strength and elasticity. In classical EDS, mutations disrupt the production or processing of type V collagen, which plays a key role in organizing collagen fibrils into properly structured bundles. When skin with this defect is injured, the fibroblasts responsible for repair produce collagen that does not assemble correctly. The result is a lump of thickened, hyalinized collagen mixed with fibrin, the clotting protein left behind from the original injury’s bleeding. Over time, repeated cycles of minor injury, poor healing, and fresh connective-tissue deposition cause the pseudotumors to grow.
These growths differ from keloids or hypertrophic scars, which also represent exaggerated healing responses. Keloids extend beyond the boundaries of the original wound and are driven by overproduction of otherwise normal collagen. Molluscoid pseudotumors, by contrast, are softer, more mobile, and reflect the structurally abnormal collagen characteristic of EDS rather than a simple excess of normal collagen. They also differ from the subcutaneous spheroids sometimes found in EDS patients: those are small, hard, calcified nodules that form within fatty tissue, while molluscoid pseudotumors are superficial and fleshy.
What Pathologists See Under the Microscope
When a molluscoid pseudotumor is biopsied and examined microscopically, the hallmark is a proliferation of fibroblasts within the dermis surrounded by thick bundles of collagen that appear glassy and homogeneous, a quality pathologists call hyalinization. Deposits of fibrin are interspersed among the collagen bundles, reflecting the hematomas that seeded the original nodule. The overall pattern is consistent with a wound-healing response that never fully resolved, as though the tissue got stuck in a loop of repair without returning to its normal architecture.2ResearchGate. Histopathological characterisation of molluscoid pseudotumour seen in Ehlers–Danlos syndrome
This histological picture is distinct enough to help confirm a diagnosis of classical EDS if the clinical picture is ambiguous. In practice, though, biopsies of these nodules are not always performed, because the combination of a soft nodule at a pressure point in a patient with hyperextensible skin and hypermobile joints is usually enough for an experienced clinician to recognize the diagnosis without cutting into fragile tissue that will heal poorly.
Beyond Classical EDS
Although molluscoid pseudotumors are most strongly linked to classical EDS, they are not exclusive to it. Researchers studying Mowat-Wilson syndrome, a rare genetic condition caused by mutations in the ZEB2 gene, have documented EDS-like features in affected patients, including skin hyperextensibility, joint hypermobility, atrophic scars, and molluscoid pseudotumors at the elbows. In a study of twelve patients with Mowat-Wilson syndrome, all had soft, velvety skin, and several exhibited the same elbow nodules that would be at home on a classical EDS checklist.3Nature. Critical involvement of ZEB2 in collagen fibrillogenesis: the molecular similarity between Mowat-Wilson syndrome and Ehlers-Danlos syndrome
The overlap makes biological sense. ZEB2 turns out to be critically involved in collagen fibrillogenesis, the process by which individual collagen molecules assemble into the fibrils that give connective tissue its strength. When ZEB2 is disrupted, collagen organization suffers in ways that parallel the defects seen in EDS. The molecular similarity explains why two genetically distinct conditions can produce the same clinical signs, including the same characteristic pseudotumors. For clinicians, this overlap means that the presence of molluscoid pseudotumors should prompt consideration of the full spectrum of connective-tissue disorders rather than an automatic diagnosis of classical EDS alone.
Why the Name Causes Confusion
The word “molluscoid” literally means “resembling molluscum,” referring to the dome-shaped, waxy bumps caused by the molluscum contagiosum virus. The molluscoid pseudotumors of EDS earned the name because their smooth, rounded appearance can superficially resemble large molluscum lesions. In clinical practice, this naming convention creates a persistent source of confusion, because many other conditions produce skin lesions that look molluscum-like, and the word “molluscoid” gets applied loosely across all of them.
True molluscum contagiosum is a viral infection caused by a poxvirus. The classic lesion is a small, flesh-colored or pearly papule with a central dimple, or umbilication. Under the microscope, the infected skin cells contain large, round inclusion bodies called molluscum bodies that are unmistakable.4PubMed. Histopathological features of molluscum contagiosum other than molluscum bodies In healthy people, these lesions are a nuisance that resolves on its own within months. In immunosuppressed individuals, however, molluscum contagiosum can become severe, widespread, and resistant to treatment, sometimes requiring medications like cidofovir or imiquimod.5PubMed. 2020 European guideline on the management of genital molluscum contagiosum The EDS-associated pseudotumors share no viral origin, no inclusion bodies, and no infectious potential with molluscum contagiosum. The resemblance is purely superficial.
Infections That Produce Molluscoid-Looking Lesions
The clinical importance of the “molluscoid” label extends beyond EDS, because several serious infections can produce skin lesions that closely mimic the appearance of either molluscum contagiosum or molluscoid pseudotumors. Recognizing these mimics is a practical diagnostic challenge, especially in immunocompromised patients where the stakes are highest.
Cryptococcosis, a fungal infection caused by Cryptococcus neoformans, can disseminate from the lungs to the skin and present as molluscoid nodules. In one reported case, disseminated cryptococcosis appeared first as skin lesions resembling molluscum before progressing to meningo-encephalitis, a life-threatening brain infection.6World Journal of Clinical Cases. Beyond the usual suspects – disseminated cryptococcosis presenting as molluscoid skin lesions: A case report This presentation is deceptive because the skin lesions look benign and self-limited, while the infection raging beneath the surface is anything but.
Talaromycosis, caused by the fungus Talaromyces marneffei (formerly known as Penicillium marneffei), is another infection whose skin manifestations classically mimic molluscum contagiosum. The hallmark is papules with a central area of dead tissue, closely imitating the dimpled surface of molluscum. This fungal infection is most common in Southeast Asia and predominantly affects people with weakened immune systems, though cases in otherwise healthy individuals have been documented.7PubMed Central. Generalized cutaneous talaromycosis (Penicilliosis) in an immunocompetent individual
Paracoccidioidomycosis, a systemic fungal infection endemic to Latin America, adds another layer to the diagnostic puzzle. When patients with HIV/AIDS develop this infection, it tends to progress rapidly and produce widespread lesions, including umbilicated skin nodules that can look molluscoid. These patients frequently have very low CD4 counts and may present with paracoccidioidomycosis as the first recognizable sign of their underlying HIV infection.8Revista da Sociedade Brasileira de Medicina Tropical. Open-access Brazilian guidelines for the clinical management of paracoccidioidomycosis
Mycobacterial Pseudotumors
Bacteria can also form pseudotumors in the skin that enter the differential diagnosis. Mycobacterial pseudotumors are an uncommon but well-documented phenomenon, particularly in transplant recipients and other patients on immunosuppressive medications. In one case involving a liver transplant recipient, a skin lesion composed mainly of spindle-shaped cells was initially suspected to be a tumor. Closer examination with special stains revealed large numbers of acid-fast bacilli within the cells, and molecular testing identified the culprit as Mycobacterium avium, a common environmental mycobacterium that rarely causes disease in people with intact immune systems.9PubMed. Mycobacterial pseudotumor of the skin
Mycobacterial pseudotumors are particularly tricky because they can mimic both benign and malignant tumors under the microscope. The spindle-cell morphology looks nothing like a typical bacterial infection and everything like a soft-tissue neoplasm. Without the specific stains that highlight mycobacteria, a pathologist might not think to look for an infectious cause. This reinforces a broader point in dermatopathology: any atypical skin nodule in an immunosuppressed patient warrants a careful search for infectious organisms before assuming a neoplastic diagnosis.
The Immunosuppression Factor
A recurring theme across the infections that mimic molluscoid pseudotumors is the role of immunosuppression. In people with healthy immune systems, molluscum contagiosum stays small and clears on its own, Cryptococcus rarely reaches the skin, and talaromycosis is uncommon. But when the immune system is compromised, whether by HIV, organ transplant medications, chemotherapy, or other causes, these infections behave differently. Molluscum contagiosum lesions grow larger and more numerous. Fungal infections disseminate from internal organs to the skin, producing molluscoid nodules that serve as visible clues to a systemic process. Mycobacteria that would normally be controlled form tumor-like masses.
HIV infection provides the starkest example. Patients with low CD4 counts are especially vulnerable to atypical presentations of molluscum contagiosum, with giant lesions appearing on the trunk and extremities that can be difficult to diagnose clinically.10European Journal of Clinical Medicine. Giant Molluscum Contagiosum Opportunistic Infection in a HIV/AIDS Patient The same patients are at risk for the fungal infections described above, creating a situation where a molluscoid skin lesion could represent any of several diagnoses, each requiring a completely different treatment. A biopsy with appropriate cultures and stains becomes essential rather than optional.
For clinicians, the practical takeaway is that molluscoid-appearing skin lesions in immunosuppressed patients should never be dismissed as simple molluscum contagiosum without investigation. The differential includes disseminated fungal infections, mycobacterial disease, and other opportunistic organisms, many of which are fatal without treatment. The skin lesion, easily seen and easily biopsied, may be the earliest accessible clue to a life-threatening systemic infection.
Living With Molluscoid Pseudotumors in EDS
For patients with Ehlers-Danlos syndrome who develop true molluscoid pseudotumors, the experience is very different from the infectious mimics. The pseudotumors themselves are painless, benign, and not dangerous. They do not require urgent treatment, and they do not signal an underlying infection or malignancy. What they do represent is a visible marker of the tissue fragility that defines the condition.
Surgical removal is possible but comes with caveats. EDS skin heals poorly. Incisions may dehisce, scars tend to widen and thin, and the fragile tissue is prone to developing new pseudotumors at the surgical site itself. For this reason, excision is generally reserved for pseudotumors that are cosmetically distressing or mechanically problematic, such as those that catch on clothing or interfere with joint movement. The decision to operate weighs the modest benefit of removing the nodule against the real risk of a wound that heals worse than the original lump.
Prevention, to the extent it exists, centers on minimizing trauma to vulnerable areas. Padding the elbows and knees during physical activity, avoiding contact sports, and treating even minor skin injuries carefully can reduce the frequency of new pseudotumors. These measures align with the broader skin-care strategy for classical EDS, where the goal is to prevent the cycle of injury and abnormal healing that drives many of the condition’s cutaneous complications.
Distinguishing Molluscoid Pseudotumors From Subcutaneous Spheroids
Patients and clinicians sometimes conflate molluscoid pseudotumors with another EDS-related finding: subcutaneous spheroids, also called spheroid bodies. Both are palpable lumps associated with classical EDS, but they are distinct entities. Subcutaneous spheroids are small, hard, round nodules that form within the fatty tissue beneath the skin, often on the forearms and shins. They represent calcified fat lobules, essentially tiny deposits of calcium within the subcutaneous fat, and they feel like small beads rolling under the skin. On X-ray, they appear as round calcified densities.
Molluscoid pseudotumors, by contrast, sit in the dermis rather than the subcutaneous fat. They are soft and fleshy, not hard and calcified. They develop at sites of trauma and scarring rather than spontaneously. And their histological composition, fibroblastic proliferation with hyalinized collagen, is entirely different from the calcified fat of spheroids. Both findings support a diagnosis of classical EDS, and both may be present simultaneously, but they reflect different aspects of the connective-tissue disorder. Recognizing the distinction matters because it influences what a clinician expects to find on biopsy and avoids unnecessary alarm when a patient discovers a new lump.
When Genetic Testing Helps
Molluscoid pseudotumors alone are not enough to diagnose EDS or any other specific genetic condition, but they are a strong clinical clue that pushes the evaluation forward. The 2017 international classification of EDS lists molluscoid pseudotumors as a minor criterion for classical EDS, alongside other skin and joint findings. When a patient presents with these nodules plus hyperextensible skin, easy bruising, widened atrophic scars, and hypermobile joints, the clinical suspicion is high enough to warrant genetic testing for mutations in COL5A1 or COL5A2, the genes encoding type V collagen.
Genetic confirmation matters for several reasons. It distinguishes classical EDS from hypermobile EDS (the most common subtype), which does not typically produce molluscoid pseudotumors and has a different prognosis for vascular and organ complications. It identifies patients who may be at risk for the rarer but more dangerous vascular complications of connective-tissue disease. And, as the Mowat-Wilson syndrome overlap demonstrates, it can reveal that the connective-tissue features are part of a broader genetic syndrome requiring a different management approach altogether.11Nature. Critical involvement of ZEB2 in collagen fibrillogenesis: the molecular similarity between Mowat-Wilson syndrome and Ehlers-Danlos syndrome A patient with molluscoid pseudotumors and unexplained developmental delay, for instance, would prompt a very different genetic workup than a patient with the same pseudotumors and a family history of joint hypermobility.