# Gum Hyperplasia in Dogs and Cats: Causes and Care Gingival hyperplasia is a reactive, non-neoplastic enlargement of the gingiva caused by proliferation of the fibrous connective tissue and epithelium in response to chronic irritation or drug exposure. It is distinct from gingival neoplasia and from epulis, which are true tumors or tumor-like growths of the periodontal tissues. Gum hyperplasia matters because it is common, it is frequently mistaken for cancer by owners, and it sits at the intersection of dentistry, pharmacology, and pathology. A dog on long-term cyclosporine for atopic dermatitis or immune-mediated disease can develop hyperplastic gingiva within weeks to months, and the decision to treat, reduce the drug, or simply monitor depends on understanding the mechanism. In one biopsy-based survey of 704 canine oral lesions, gingival hyperplasia accounted for 23.6% of all non-neoplastic lesions, making it the single most common non-cancerous oral pathology in that cohort [1]. A separate retrospective study of 486 oral lesions in dogs and cats found that 23.24% of canine cases were diagnosed with gingival hyperplasia [2]. In dogs, it is the most frequent non-neoplastic oral lesion overall [3]. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## What Gingival Hyperplasia Actually Is ### A Reactive Process, Not a Neoplasm The defining feature of gingival hyperplasia is that it is reactive. The tissue grows because something is stimulating it, not because a clone of cells has escaped normal growth control. Histologically, the lesion consists of thickened connective tissue with increased numbers of fibroblasts and a variable inflammatory infiltrate [4]. The epithelium overlying this fibrous core may be acanthotic (thickened) and the junctional epithelium can extend into the lesion, a finding interpreted as a hyperplastic rather than neoplastic response [5]. This distinction is not academic. Reactive lesions stop growing when the stimulus is removed. In one documented case, a 7-year-old longhaired dachshund receiving cyclosporine for 600 days developed gingival mass lesions that regressed and disappeared when the drug dose was markedly decreased [6]. Neoplasms do not behave this way. ### The Terminology Problem Veterinary dentistry uses several overlapping terms, and students routinely confuse them. Hyperplastic gingiva refers to the enlarged tissue itself. Gingivitis hyperplasia describes the combination of inflammation and proliferation that occurs when plaque accumulates on a hyperplastic surface. Gum hyperplasia is the lay term. All three describe the same reactive process at different stages or with different emphasis. The confusion with epulis is more serious. Epulis is a clinical descriptor for a gingival mass, not a diagnosis. The most common epulis in dogs is fibromatous epulis of periodontal ligament origin (FEPLO), also called peripheral odontogenic fibroma (POF). A 2026 histomorphologic study of 100 canine FEPLO/POF lesions found that 88% attached to alveolar bone, 63% contained odontogenic epithelium, and 54% had bone or cemento-osseous matrix [5]. The authors proposed that these lesions are better understood as hyperplastic rather than truly neoplastic, and suggested the unifying name "fibromatous hyperplasia of the gingival ligament" [5]. This does not mean FEPLO and gingival hyperplasia are the same condition. It means both sit on a spectrum between reactive proliferation and benign neoplasia, and the boundary is defined by histopathology. ### Summary Table: Gingival Hyperplasia vs. Its Mimics | Feature | Gingival Hyperplasia | Epulis (FEPLO/POF) | Gingival Neoplasia | |--|--|--|--| | Behavior | Reactive, reversible | Benign, slow-growing | Variable, may be malignant | | Cause | Plaque, drug, breed predisposition | Uncertain, likely hyperplastic | Genetic, viral, unknown | | Histology | Fibrous tissue, inflammatory infiltrate, no odontogenic epithelium | Fibrous tissue, odontogenic epithelium (63%), bone/cementum (54%) [5] | Atypical cells, mitotic figures, invasion | | Response to stimulus removal | Regresses | Does not regress | Progresses | | Most common in | Boxer, Bulldog, Collie, Great Dane | Any breed | Any breed, older dogs | | Treatment | Gingivectomy if pseudopockets form | Surgical excision | Surgical excision, oncology workup | ## Mechanisms of Gingival Enlargement ### Plaque-Driven Hyperplasia The most common mechanism is chronic plaque irritation. Bacteria in plaque stimulate a sustained inflammatory response in the gingival margin. Inflammatory cytokines recruit fibroblasts and promote collagen synthesis. Over time, the gingiva thickens and loses its normal scalloped contour. This is the same process that causes gingival overgrowth in people with poor oral hygiene, and it is entirely reversible with plaque control if the fibrous component has not yet matured. Once the tissue becomes predominantly fibrous, it will not shrink with brushing alone. This is why early intervention matters. ### Drug-Induced Hyperplasia Three drug classes are consistently associated with gingival overgrowth in veterinary and laboratory animal medicine: immunosuppressants (cyclosporine), anticonvulsants (phenytoin), and calcium channel blockers (nifedipine, amlodipine, felodipine) [7]. The mechanism is not fully understood, but several pathways have been proposed. Cyclosporine appears to act through direct effects on gingival fibroblasts. The drug stimulates fibroblast proliferation and collagen synthesis while inhibiting collagenase activity, tipping the balance toward matrix accumulation. A study in beagle dogs found that gingival enlargement developed in 5 of 12 dogs (42%) during daily cyclosporine treatment, with the earliest changes appearing by week 3 as enlargement of the interdental papillae [8]. Both incidence and severity correlated with cyclosporine blood concentration. The mean blood levels of responders were significantly higher than nonresponders at weeks 3, 6, and 10 [8]. Phenytoin, an anticonvulsant, produces a similar pattern. A case report described an adult male lowland gorilla treated with diphenylhydantoin for 6 months that developed acute inflammatory gingival hyperplasia severe enough to cause anorexia. Full mouth gingivectomy resolved the oral inflammation and the animal resumed eating [9]. Calcium channel blockers may act through a different mechanism involving aldosterone suppression and subsequent androgen accumulation. One hypothesis proposes that calcium channel blockade in the adrenal zona glomerulosa reduces aldosterone synthesis, triggering compensatory ACTH secretion and accumulation of steroid intermediates that are converted to testosterone. Elevated testosterone then acts on gingival cells to produce hyperplasia [10]. A 12-month toxicity study of felodipine in dogs found noninflammatory gingival hyperplasia similar to that seen with phenytoin and nifedipine, with a propensity for males [11]. ### The Role of Plaque in Drug-Induced Cases Plaque is not required for drug-induced gingival overgrowth to begin, but it worsens the severity. In the rat model, accumulation of dental plaque was not essential for onset but played a role in severity [7]. This has practical implications. A dog on cyclosporine with excellent oral hygiene may develop only mild hyperplasia, while a dog with existing periodontal disease may develop severe overgrowth. ## Drug Causes in Detail ### Cyclosporine Cyclosporine is the most clinically important drug cause of gingival hyperplasia in dogs. It is used for atopic dermatitis, perianal fistulas, immune-mediated diseases, and as part of immunosuppressive protocols after renal transplantation [4][12][13]. The relationship between dose and hyperplasia is well documented. In a canine renal transplantation model, dogs received microemulsified cyclosporine at 20 mg/kg/day with whole blood trough concentrations maintained at 400 to 700 ng/mL. Gingival hyperplasia developed in 3 of 4 dogs, with the earliest changes in the interdental papillae at 20 weeks [4]. In a study of dogs with naturally occurring glomerulonephritis, cyclosporine was dosed to maintain trough concentrations between 250 and 400 ng/mL [14]. At lower doses used for dermatology, the incidence is lower but still significant. A retrospective study of 48 dogs treated with cyclosporine for presumed idiopathic chronic hepatitis found that gingival hyperplasia occurred in 25% of treated dogs [15]. In a long-term safety review of cyclosporine for canine atopic dermatitis, gingival hyperplasia was listed among adverse events that were rarely significant and resolved on dose reduction [12]. Another dermatology review noted that gingival hyperplasia, verruciform lesions, and hypertrichosis appear to be dose-dependent [13]. This dose dependence is the key clinical fact. Cyclosporine-induced gingival hyperplasia may regress with dose reduction. If dose reduction is not possible because of the underlying disease, switching to tacrolimus is an option. Tacrolimus is a calcineurin inhibitor like cyclosporine but has a different adverse effect profile. One study of dogs receiving calcineurin inhibitors found that 4 of 28 dogs had gingival hyperplasia or paw-pad hyperkeratosis, and 4 dogs received topical tacrolimus [16]. The study did not establish that tacrolimus causes less gingival hyperplasia, but the option is worth discussing with a veterinary dermatologist or internist when cyclosporine is the suspected cause. ### Phenytoin Phenytoin is rarely used in [veterinary medicine](/blog/careers/veterinary-medicine-careers-from-clinical-practice-to-public-health) today, but it remains a recognized cause of gingival hyperplasia across species. The gorilla case demonstrates that the effect is not limited to dogs and cats [9]. The mechanism is similar to cyclosporine, involving direct fibroblast stimulation and collagen accumulation. ### Nifedipine and Other Calcium Channel Blockers Nifedipine, amlodipine, and felodipine have all been associated with gingival hyperplasia. A 12-month study in dogs found that felodipine caused noninflammatory gingival hyperplasia with a male predisposition [11]. The proposed mechanism involves adrenal steroidogenesis and androgen accumulation [10]. These drugs are used in veterinary medicine for hypertension and cardiac disease, so the possibility of gingival overgrowth should be considered in any dog on long-term calcium channel blocker therapy. ## Breed Predilections Certain breeds develop gingival hyperplasia more frequently than others. The Boxer, Bulldog, Collie, and Great Dane are overrepresented in clinical practice. This predilection likely reflects a genetic predisposition to exaggerated fibrous response to plaque. A case report described an 8-year-old Boxer with generalized gingival hyperplasia and multiple gingival masses. Three masses were biopsied, and microscopic examination revealed fibrous gingival hyperplasia, fibrous epulis with osseous metaplasia, and mast cell tumor in the same dog [17]. Twenty-two months after surgery, moderate generalized gingival hyperplasia was present, but there was no clinical evidence of regrowth of the neoplasms [17]. This case illustrates two important points. First, breed predisposition to hyperplasia does not protect against neoplasia. Second, hyperplastic gingiva can coexist with tumors, so any suspicious mass should be biopsied even in a breed known for reactive lesions. ## How Gingival Hyperplasia Is Diagnosed ### Clinical Examination Diagnosis begins with visual inspection. Hyperplastic gingiva appears as thickened, firm, often lobulated tissue that may cover part of the tooth crown. The surface may be smooth or irregular. The color ranges from normal pink to reddened if inflammation is present. The interdental papillae are often the first area affected, as seen in the cyclosporine studies [4][8]. A complete oral examination under anesthesia is usually necessary to assess the full extent of the lesion, probe for pseudopockets, and evaluate underlying bone. Pseudopockets are spaces between the hyperplastic gingiva and the tooth surface that are not true periodontal pockets because the attachment apparatus is intact. They trap plaque and perpetuate inflammation. ### Biopsy Biopsy is indicated when the lesion is rapidly growing, ulcerated, or has an atypical appearance. Histopathology distinguishes gingival hyperplasia from neoplasia and from epulis. The characteristic findings in hyperplasia are thickened connective tissue with increased fibroblasts and inflammatory infiltrate [4]. In cyclosporine-associated cases, the histologic diagnosis may be reported as hyperplastic suppurative gingivitis [6]. A study investigating canine papillomavirus 1 (CPV1) in oral lesions tested 10 hyperplastic gingival lesions and found no viral DNA or L1 protein, confirming that CPV1 is not involved in gingival hyperplasia [18]. This is relevant because oral papillomatosis is a common concern in young dogs, and the distinction matters for prognosis and treatment. ### When to Suspect Drug-Induced Hyperplasia Any dog or cat on cyclosporine, phenytoin, or a calcium channel blocker that develops gingival enlargement should be suspected of drug-induced hyperplasia. The temporal relationship is important. Cyclosporine-induced changes can appear as early as 3 weeks after starting treatment [8], though in the renal transplantation model the earliest changes were at 20 weeks [4]. The difference likely reflects dose and blood concentration. ## Table: Causes and Clinical Approach | Cause | Typical History | Clinical Appearance | Diagnostic Approach | Management | |--|--|--|--|--| | Plaque-induced | Chronic poor oral hygiene, no drug history | Generalized or localized thickening, reddened gingival margin | Oral exam, probing, radiographs | Gingivectomy if pseudopockets, plaque control | | Cyclosporine | On cyclosporine for weeks to months | Interdental papillae enlargement, may progress to cover teeth | Drug history, biopsy if atypical | Dose reduction, switch to tacrolimus, gingivectomy | | Phenytoin | On anticonvulsant therapy | Similar to cyclosporine | Drug history, biopsy | Dose reduction or drug change, gingivectomy | | Calcium channel blocker | On nifedipine, amlodipine, or felodipine | Noninflammatory hyperplasia, male predisposition | Drug history, biopsy | Dose reduction or drug change, gingivectomy | | Breed-associated | Boxer, Bulldog, Collie, Great Dane | Generalized fibrous hyperplasia | Breed history, biopsy if masses present | Gingivectomy, aggressive plaque control | | Epulis (FEPLO/POF) | Any breed, often older dogs | Solitary mass, may have bone/cementum | Biopsy required | Surgical excision | | Gingival neoplasia | Any breed, rapid growth, ulceration | Irregular, friable, may invade bone | Biopsy required | Oncology workup, surgical excision | ## Treatment: When to Treat vs. When to Monitor ### Monitoring Mild gingival hyperplasia that does not cover the tooth crown, does not trap plaque, and does not cause discomfort can be monitored. This is particularly true for drug-induced cases where dose reduction may resolve the lesion. In the dachshund case, gingival masses disappeared when cyclosporine dose was decreased [6]. In the cyclosporine safety review, gingival hyperplasia resolved on dose reduction [12]. Monitoring should include regular oral examinations, assessment of plaque accumulation, and documentation of lesion size. Photographs are helpful for tracking progression. ### Gingivectomy and Gingivoplasty Surgical treatment is indicated when hyperplasia creates pseudopockets that trap plaque, when the tissue covers the tooth crown enough to interfere with eating or occlusion, or when the lesion is cosmetically unacceptable to the owner. Gingivectomy removes the excess tissue. Gingivoplasty reshapes the gingival contour. Both are performed under general anesthesia. The goal is to eliminate pseudopockets and restore a normal gingival margin that can be kept clean by brushing. If the underlying cause is not addressed, recurrence is likely. In the Boxer case, moderate generalized gingival hyperplasia was present 22 months after surgery, even though the neoplasms did not regrow [17]. ### Plaque Control Plaque control is the single most important factor in reducing recurrence. This includes daily brushing, veterinary dental diets, chews, and professional cleanings. In drug-induced cases, plaque control may not prevent the initial onset but reduces severity [7]. In plaque-induced cases, plaque control is curative if the fibrous component has not matured. ### Addressing the Underlying Cause For drug-induced hyperplasia, the ideal treatment is to reduce or discontinue the offending drug. This requires coordination with the veterinarian managing the primary disease. Cyclosporine dose reduction may be possible for atopic dermatitis but not for life-saving immunosuppression after transplantation. In those cases, gingivectomy may be repeated as needed, and plaque control becomes even more critical. ## Clinical Relevance, Limitations and Common Mistakes Gingival hyperplasia is clinically relevant because it is common, it mimics cancer, and it is often iatrogenic. The most common mistake is assuming that a gingival mass in a dog is benign because the dog is a Boxer or because the dog is on cyclosporine. The Boxer case demonstrated that hyperplasia, epulis, and mast cell tumor can coexist in the same mouth [17]. Any mass that is rapidly growing, ulcerated, or atypical should be biopsied. Another common mistake is failing to recognize drug-induced hyperplasia. A dog on cyclosporine for atopic dermatitis that develops gingival enlargement may be treated with gingivectomy without any attempt to reduce the drug dose. This leads to recurrence and repeated anesthesia. The dose-dependent nature of cyclosporine-induced hyperplasia means that dose reduction should always be considered first if the primary disease allows it [12][13]. A third mistake is confusing gingival hyperplasia with epulis. Epulis is a clinical term for a gingival mass, not a diagnosis. FEPLO/POF is the most common benign oral tumor in dogs, accounting for 81.3% of benign neoplasms in one survey [1]. It requires surgical excision, not just plaque control. Limitations of current knowledge include an incomplete understanding of why some dogs develop hyperplasia on cyclosporine and others do not. The beagle study found that only 42% of dogs developed overgrowth despite similar dosing [8]. Genetic factors, local oral environment, and individual fibroblast sensitivity likely play roles. The exact mechanism of calcium channel blocker-induced hyperplasia remains hypothetical [10]. Individual cases require veterinary assessment. This article provides general information, not a diagnosis or treatment plan. ## Quick Review 1. Gingival hyperplasia is a reactive fibroepithelial proliferation, not a neoplasm. It regresses when the stimulus is removed. 2. Drug causes include cyclosporine, phenytoin, and calcium channel blockers (nifedipine, amlodipine, felodipine). 3. Cyclosporine-induced hyperplasia is dose-related and may regress with dose reduction or switching to tacrolimus. 4. Breed predilections include Boxer, Bulldog, Collie, and Great Dane. 5. Treatment is gingivectomy or gingivoplasty when pseudopockets trap plaque. 6. Plaque control reduces recurrence. 7. Biopsy any rapidly growing, ulcerated, or atypical gingival mass to rule out neoplasia or epulis. ## Frequently Asked Questions ### What is the difference between gingival hyperplasia and gum cancer? Gingival hyperplasia is a reactive enlargement of the gums that is not cancerous. Gum cancer, such as oral melanoma or squamous cell carcinoma, involves malignant cells that invade and destroy tissue. A biopsy is the only way to tell them apart. ### Can cyclosporine cause gum hyperplasia in dogs? Yes. Cyclosporine is a well-documented cause of gingival hyperplasia in dogs, and the effect is dose-related. Reducing the dose or switching to another medication may resolve the hyperplasia. ### Which dog breeds are most prone to gingival hyperplasia? Boxers, Bulldogs, Collies, and Great Danes are overrepresented. These breeds appear to have a genetic predisposition to exaggerated fibrous response to plaque. ### When does gingival hyperplasia need surgery? Surgery is needed when the hyperplastic tissue creates pseudopockets that trap plaque, covers the tooth crown enough to interfere with eating, or causes discomfort. Mild cases that do not trap plaque can be monitored. ### Does brushing help gingival hyperplasia? Brushing helps reduce plaque, which reduces the severity of hyperplasia and the risk of recurrence after surgery. It does not reverse mature fibrous hyperplasia. ### Can gingival hyperplasia go away on its own? Yes, if the underlying cause is removed. Drug-induced hyperplasia may regress when the drug is reduced or discontinued, and plaque-induced hyperplasia may improve with excellent oral hygiene before the tissue becomes predominantly fibrous. ## Related Articles - [How To Treat Gum Disease In Dogs](/knowledge/veterinary-medicine/dental-care/how-to-treat-gum-disease-in-dogs) - [Dog Pale Gums: What Does It Mean?](/knowledge/veterinary-medicine/emergency-care/dog-pale-gums-meaning) - [Cat Diarrhea: Causes, Home Care, and When to Worry](/knowledge/veterinary-medicine/online-vet-and-care-costs/cat-diarrhea-causes-home-care) - [Dog Ate Sugar-Free Gum: What Should You Do?](/knowledge/veterinary-medicine/toxicology-and-food-safety/dog-ate-sugar-free-gum) - [My Dog Ate a Cigarette or Nicotine Gum: What Should I Do?](/knowledge/veterinary-medicine/vet-visit-decisions/dog-ate-cigarette-nicotine-gum) - [Budgie Respiratory Infection: Signs, Causes, and Urgent Care](/knowledge/veterinary-medicine/pet-bird-care/budgie-respiratory-infection) - [Keratosis Pilaris Causes: Follicular Plugging Explained](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/keratosis-pilaris-causes-follicular-plugging-explained) - [Dropped Jaw in Dogs: Causes and What to Do](/knowledge/veterinary-medicine/symptom-guides/dropped-jaw-in-dogs-causes-and-what-to-do) - [Dog Digestive Issues: Causes, Symptoms, and When to Worry](/knowledge/veterinary-medicine/digestive-and-urinary-care/dog-digestive-issues-causes-symptoms-and-when-to-worry) ## Sources 1. 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