Labial calcinosis circumscripta in a dog with history of Hymenopteran stings in oral cavity - case report

[Calcinose circunscrita labial em um cão com histórico de picada por himenópteros na cavidade oral - relato de caso]

ABSTRACT

Calcinosis circumscripta (CC) is a benign lesion characterized by focal-to-multifocal mineralized deposits mainly in the cutaneous and subcutaneous tissues. CC is uncommon in the oral cavity of dogs and its etiopathogenesis is unclear. Its differential diagnosis includes non-proliferative to neoplastic lesions that course with leukoplakia in the oral mucosa. This study describes the case of a 2-year-old male Shih-Tzu dog, who presented with increased volume on the inner surface of the lower lip and a history of Hymenoptera (bee and wasp) stings at the site of the injury. The lesion was diagnosed via excisional biopsy based on the gross and microscopic characteristics. In addition to contributing to the differential diagnosis of lesions with leukoplakia in the oral mucosa of dogs, to the best of our knowledge, this is the first report of labial CC in a dog with history of Hymenopteran stings suggesting a potential complication of Hymenopteran venom-induced lesions in the oral cavity of dogs.

Keywords:
calcification; calcium; dog; dystrophic calcification; oral lesion

RESUMO

Calcinose circunscrita (CC) é uma lesão benigna, caracterizada por deposição focal a multifocal de minerais, principalmente em tecidos cutâneo e subcutâneo. CC é incomum na cavidade oral de cães e a etiopatogenia da lesão é indeterminada. O diagnóstico diferencial da CC oral inclui lesões não proliferativas a neoplásicas que cursam com leucoplasia na mucosa oral. Este estudo descreve o caso de um cão da raça Shih-Tzu, macho, de 2 anos de idade, que apresentou aumento de volume na superfície interna do lábio inferior e histórico de picadas de Hymenoptera (abelha e vespa) no local da lesão. A lesão foi diagnosticada por biópsia excisional, a partir das características macroscópicas e microscópicas. Além de contribuir para o diagnóstico diferencial de lesões com leucoplasia na mucosa oral de cães, até onde se sabe, este é o primeiro relato de CC labial em um cão com histórico de picadas de himenópteros, sugerindo uma potencial complicação de lesões induzidas por veneno de hymenópteros na cavidade oral de cães.

Palavras-chave:
calcificação; cálcio; cães; calcificação distrófica; lesão oral

INTRODUCTION

Calcinosis circumscripta (CC; syn. tumoral calcinosis) is a benign lesion characterized by focal to multifocal calcification in soft tissues (Gross et al., 2005; Lee et al., 2016; Mauldin and Peters-Kennedy, 2016; Munday et al., 2017; Heirich et al., 2018; Haynes, 2023). Morphologically, CC is characterized by focal-to-multifocal accumulation of mineralized amorphous material, surrounded by a granulomatous inflammatory response and fibrosis (Mauldin & Peters-Kennedy, 2016; Munday et al., 2017; Heirich et al., 2018; Mikiewicz et al., 2019; Haynes, 2023).

In dogs, CC primarily affects young animals of large breeds and occurs in the subcutaneous tissues of high-friction areas on the body (Tafti et al., 2005; Doerr et al., 2013; Mauldin and Peters-Kennedy, 2016; Lee et al., 2016; Heirich et al., 2018; Delgado et al., 2023). The etiopathogenesis of CC is not fully understood; however, previous traumatic injuries, dystrophic or metastatic calcifications, or idiopathic factors may contribute to its development (Tafti et al., 2005; Doerr et al., 2013; Lee et al., 2016; Mauldin and Peters-Kennedy, 2016; Heirich et al., 2018; Lobprise, 2019).

In the oral cavity, CC lesions exhibit morphological characteristics similar to those found in other parts of the body and can mimic proliferative or pseudotumor lesions (Munday et al., 2017; Villa and Woo, 2017; Anderson, 2023). While cases of oral CC in dogs have been reported since the 1960s (Cotchin, 1960; Douglas and Kelly, 1966), these lesions are known to occur predominantly on the tongue, although the etiopathogenesis of oral CC remains unclear (Lee et al., 2016; Munday et al., 2017; Anderson, 2023; Collados et al., 2002; Delgado et al., 2023). Recently, Santos et al. (2022) described a case of CC in the oral cavity of a cat secondary to a wasp (Hymenoptera vespidae) sting.

In humans, oral leukoplakia is a clinical term applied to a group of oral mucosa lesions, characterized by whitish patches or plaques that may be proliferative or potentially malignant (Villa and Woo, 2017). In dogs, although rare, oral leukoplakia can occur due to various conditions, including idiopathic lesions, chronic ulcerative stomatitis, granulomatous inflammation (caused by parasites or foreign bodies) with secondary calcification, eosinophilic granuloma, lichenoid reactions, foamy cell histiocytosis, mucus membrane pemphigoid, xanthoma, calcinosis circumscripta, and neoplasms (Gross et al., 2005; Anderson, 2023). Differential diagnosis of conditions with oral leukoplakia can be challenging upon physical examination due to nonspecific clinical signs and morphological similarities in lesion presentation (Anderson, 2023). In this sense, history and histopathological examination is important for confirming the diagnosis of oral CC (Munday et al., 2017; Villa and Woo, 2017; Anderson, 2023).

The present study aimed to describe a case of labial CC in a dog with a history of Hymenopteran (Order Hymenoptera) stings.

A 2-year-old male Shih-Tzu dog was admitted for clinical evaluation due to a tumor on the inner surface of the lower lip located in the labial vestibule near the gingival mucosa junction. The labial lesion had been progressively growing over the course of 1 month prior to admission. The owner reported that the dog had been stung twice on the lip, once by a bee (Hymenoptera anthophila) and once by a wasp (H. vespidae); however, she was unable to specify the exact timing of these incidents.

On physical examination, the dog was found to be healthy, with up-to-date vaccinations and ectoparasite control, and no relevant history of illness and/or previous surgical procedures. Surgical removal of the lesion was recommended.

Preoperative hematological and serum biochemical tests were conducted, revealing normal blood count parameters for the species. The only notable findings were a slight increase in hemoglobin (19.80g/dL; reference value: 12.0- 18.0g/dL). Serum biochemistry indicated a slight increase in alanine aminotransferase (78.60 IU/L; reference value: 21.0-73.0 IU/L) while the values of alkaline phosphatase, total protein, albumin, creatinine, and urea were within normal limits. Additionally, pre-surgical cardiological assessments, including an echocardiogram and electrocardiogram, showed normal physiology and sinus rhythm, respectively.

The surgery consisted of excision of the lesion in the lower lip, with a wide trichotomy and antisepsis with 2% aqueous Chlorhexidine of the rostral region of the mandible using monocryl 3-0 absorbable suture. Conventional oral drug therapy with analgesics, anti-inflammatories and antibiotics were prescribed post-surgery, in addition to topical medications to assist in the healing of the surgical wound.

Macroscopic evaluation revealed a domed mass on the inner surface of the lip, measuring 1.2×1.0×0.7cm, with a firm and intact appearance. The cut surface was multilobed and presented multiple foci of accumulated white material with a chalky texture (Fig. 1).

Figure 1
Dog, lower lip (external and internal surfaces), cut surface, formalin-fixed, paraffin-embedded tissue. On the inner surface of the lip there is a multilobulated lesion, with an accumulation of white material.

Tissue fragments obtained by the excisional biopsy were fixed in 10% formaldehyde, processed using routine paraffin embedding techniques, and the histopathological sections (5 µm) were stained in hematoxylin-eosin, Von Kossa, Gram, and Ziehl-Neelsen stains. Histological examination was conducted using a light microscope (Eclipse Ni-U, Nikon, Tokyo, Japan) and a photodocumentation system (DS-U3 cooled digital camera, Nikon, Tokyo, Japan; and NiS elements F 4.00.00 software).

Microscopically, the external surface of the lip showed a preserved morphology (Figure 2a), but the submucosa of the internal surface of the lip showed a well-defined, multilobulated lesion with multifocal to coalescent areas of basophilic, amorphous, and fragmented material deposition, which are characteristic of calcium salt deposits (Figure 2b). The foci of calcification were surrounded by a moderate granulomatous inflammatory response composed of numerous epithelioid macrophages and occasional foreign body-type multinucleated giant cells. Moderate fibroplasia was also observed between the areas of calcification and granulomatous inflammation (Figures 2c and 2d).

Figure 2
Dog, lower lip. a) External surface of the lip with preserved morphology. Hematoxolin-eosin (HE), bar 200µm. b) Deposition of basophilic material in the submucosa of the inner surface of the lip, HE, bar 200µm; c) Inside the lesion there are multifocal to coalescent deposits of basophilic, fragmented material, surrounded by granulomatous inflammation and interspersed with moderate fibroplasia. HE, bar 200µm; d) Epithelioid macrophages and multinucleated giant cells around areas of mineralization. HE, bar 50µm.

The nature of the basophilic material (calcification) was confirmed by Von Kossa histological staining, and negative Gram and Zeehl-Neelsen staining ruled out the involvement of bacterial agents in the etiology of the lesion (Figures 3a and 3b). The morphological diagnosis of CC was established based on the gross and microscopic patterns of lip lesion.

Seventeen days post-surgery, the animal was in good condition with satisfactory wound healing. Complications were limited to the softening of lower right central incisor tooth, with no impact on feeding. The owners reported normorexia, normodipsia, normochesia, and unchanged urine.

Complementary post-surgical venous blood gas analysis tests (ionized calcium, sodium, potassium, chlorine and bicarbonate) to assess metabolic and/or endocrine disorders that could be associated with labial circumscribed calcinosis were inconclusive as the owner abandoned the follow-up.

Figure 3
Dog, lower lip. a) Calcium deposits stained black. Von Kossa, bar 200 µm; b) Negativity of acid-fast bacilli in areas of granulomatous inflammation and calcification. Zeehl-Neelsen, bar 100 µm.

DISCUSSION

Oral CC in dogs has been described since the 1960s; however, the etiopathogenesis of this process is still unclear (Cotchin, 1960; Douglas and Kelly, 1966; Collados et al., 2002; Munday et al., 2017; Lobprise, 2019). In the recent report that described oral CC on the labial commissure of a domestic cat, the lesion had a course of approximately 6 months after the Hymenopteran sting (H. vespidae) (Santos et al., 2022). Despite the previous records of oral CC in dogs, we believe that the present case represents the first record of this type of lesion in a canine with a history of hymenoptera sting.

In the current study, although the lesion on the lips differed from the typical location (tongue) of oral CC described in dogs (Lee et al., 2016; Munday et al., 2017; Anderson, 2023; Collados et al., 2002; Delgado et al., 2023), the morphological characteristics of oral CC were similar to those described in previous studies of lesions in the oral cavity or skin (Mauldin and Peters-Kennedy, 2016; Munday et al., 2017; Heirich et al., 2018; Mikiewicz et al., 2019; Haynes, 2023). Notably, unlike in cats, ulceration was absent above the foci of calcification (Santos et al., 2022).

Hymenopteran venom can induce self-limiting local effects such as pain, edema, and erythema, typically resolving within a day; subsequent microscopic lesions at the site of an isolated sting may be absent, discrete, or nonspecific (Fitzgerald and Flood, 2006). However, in humans, there have been cases of delayed local response with necrosis of the skin and soft tissues 2-3 weeks after a Hymenopteran sting (Koçer et al., 2003). While no previous association between Hymenoptera venom-induced inflammation and local necrosis progressing to oral CC in dogs is known, mechanisms of dystrophic calcification suggest a potential pathway. Notably, soft tissue calcification secondary to Hymenoptera stings has been observed in children (Liu et al., 2018), suggesting a potential link with oral CC as seen in the previous report involving a cat with similar history and lesions (Santos et al., 2022).

The diagnosis of oral leukoplakia lesions based only on visual inspection during physical examination may not be accurate, emphasizing the importance of histopathology and clinical history for definitive diagnosis (Anderson, 2023). In the present case, although the pathogenesis of lesion development remains undetermined, the pattern of granulomatous inflammation with foreign body-type giant cells and calcification suggests a strong association with the animal's previous Hymenoptera stings at the site of the CC lesion.

In addition to local effects, Hymenopteran venom can trigger dose-dependent systemic immune-mediated responses (Fitzgerald and Flood, 2006). In the event of anaphylaxis, which usually occurs approximately 15 min after a sting injury, animals may experience respiratory dysfunction, vomiting, weakness, and convulsions (Fitzgerald, 2006; Caldwell et al., 2018). In domestic carnivores, delayed systemic effects of Hymenopteran stinging, which are uncommon and severe, can lead to hemolysis, rhabdomyolysis, hemorrhage, acute tubular injury, and neurological dysfunctions (Fitzgerald and Flood, 2006; Oliveira et al., 2007; Caldwell et al., 2018). However, in the present case, no systemic changes were observed despite the history of stings.

Cutaneous or subcutaneous CC can have various etiologies, including iatrogenic, idiopathic, dystrophic, or metastatic calcification (Gross 2005). Chronic renal failure is identified as a pathway for the development of subcutaneous CC due to disturbances in the metabolism of calcium and phosphorus (Gross 2005). Although an in-depth assessment of the animal's calcium metabolism was not feasible, hematological and biochemical tests did not indicate serious liver and/or kidney dysfunction that could explain the CC development.

Treatment for oral CC varies according to etiology, with complete surgical excision often being curative without recurrence (Munday et al., 2017). In the present case, the animal showed a good prognosis until the follow-up period, without significant complications.

CONCLUSIONS

The anatomopathological characteristics of labial CC in the present case may aid in the differential diagnosis of calcified nodular oral lesions or leukoplakia in dogs and cats. The occurrence of oral CC in the dog suggests a potential complication and delayed local effect of Hymenoptera stings in the oral cavity of small animals, warranting further investigation.

ACKNOWLEDGMENTS

We thank the technical staff of the Veterinary Teaching Hospital at Universidade Santo Amaro who contributed to the study.

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Publication Dates

• Publication in this collection
  28 Apr 2025
• Date of issue
  May-Jun 2025

History

• Received
  17 July 2024
• Accepted
  25 Nov 2024