Idiopathic multifocal calcinosis cutis presenting in a cat with vestibular syndrome: clinical,radiographic and histopathological findings

Abstract

Case summary

A 2-year-old spayed female British Shorthair cat was presented with an acute onset of right-sided head tilt, circling and horizontal nystagmus. Neurological examination, CT and video-otoscopic evaluation confirmed a right-sided peripheral vestibular syndrome secondary to otitis media. The cat received cefixime (10 mg/kg PO q24h) and methylprednisolone (1 mg/kg PO q24h) for 2 weeks, resulting in marked improvement of vestibular signs by day 4. During the physical examination, multiple firm, non-painful subcutaneous nodules of varying sizes were palpated in different body regions, unrelated to the primary neurological complaint. Laboratory analysis revealed serum calcium, ionised calcium and phosphorus concentrations within reference intervals, with a calcium–phosphorus product below the threshold for metastatic calcification. Ultrasonographic and hormonal assessments excluded metabolic, iatrogenic and dystrophic causes. Histopathological examination of an excisional biopsy from the largest lesion revealed dermal collagen fibril calcification surrounded by a hypocellular fibrous capsule and mild lymphohistiocytic inflammation, consistent with calcinosis cutis.

Relevance and novel information

The clinical, laboratory and histopathological findings supported a diagnosis of multifocal idiopathic calcinosis cutis. To the authors’ knowledge, this is the first report from Türkiye describing multifocal subcutaneous idiopathic calcinosis cutis in a cat. This case emphasises the importance of thorough physical examinations to detect concurrent, clinically silent dermatological conditions during neurological evaluations.

Plain language summary

Idiopathic multifocal calcinosis cutis in a cat with vestibular syndrome

A 2-year-old spayed female British Shorthair cat was presented with acute vestibular signs caused by otitis media. Clinical examination also revealed multiple firm, non-painful subcutaneous nodules in several body regions that were unrelated to the neurological signs. Serum calcium and phosphorus values were within reference intervals, and metabolic or iatrogenic causes were excluded. Histopathological examination of one lesion confirmed calcinosis cutis. The vestibular signs improved with medical treatment, while the cutaneous lesions remained stable. This case was diagnosed as multifocal idiopathic calcinosis cutis. To the authors’ knowledge, this is the first report from Türkiye describing a multifocal presentation in a cat. The case highlights the value of thorough physical examination in identifying clinically silent concurrent conditions.

Introduction

Calcinosis cutis is a rare condition in cats, defined by the deposition of insoluble inorganic calcium salts within the skin and/or subcutaneous tissue. From an aetiological perspective, calcinosis cutis is classified as metastatic, iatrogenic, dystrophic or idiopathic. ¹

In dogs, the most frequently encountered form is dystrophic calcification, which develops in damaged or inflamed skin tissues despite normal serum calcium and phosphorus concentrations. ² In cats, however, the most commonly reported aetiology is metastatic calcification.^{3 –5} Metastatic calcinosis is characterised by calcium deposition secondary to a metabolic disorder and is generally associated with elevated serum calcium–phosphorus levels. ⁴ A solubility product (Ca × P >70 mg²/dl²), particularly in cases such as chronic kidney disease, is often associated with mineral deposition. ⁴

Iatrogenic calcinosis has been reported to occur after calcium injection (subcutaneous or intravenous) due to percutaneous penetration or absorption of calcium salts and may occur during the treatment of disorders that can cause hypocalcaemia in cats. ⁶

In the present case report, multifocal subcutaneous calcinosis cutis was identified in the dorsal thoracic region of a 2-year-old spayed British Shorthair cat with peripheral vestibular syndrome secondary to otitis media, unrelated to the primary neurological signs. To the authors’ knowledge, this is the first case report from Türkiye describing idiopathic calcinosis cutis in a cat, and, in contrast to previously reported cases in the literature, the first to document a multifocal presentation.

The aim of this report is to present the clinical, histological and laboratory findings obtained during the aetiological work-up of multifocal idiopathic calcinosis cutis in a cat and to discuss these findings in the context of previously published cases.

Case description

A 2-year-old spayed female British Shorthair cat, weighing 3.8 kg, was presented to the Veterinary Hospital of Ondokuz Mayıs University on 24 April 2025 with a 2-day history of right-sided head tilt, right-sided circling and ataxia. The owner reported that the cat had been adopted approximately 6 months earlier, with no known history of chronic illness or regular medication. The genetic background was unknown, and there was no information suggestive of hereditary disorders.

On clinical examination, the cat exhibited vestibular ataxia and bilateral horizontal nystagmus. Palpation revealed multiple firm, non-painful subcutaneous masses of varying sizes located in different body regions. For a comprehensive evaluation, haematological and biochemical analyses, radiographic imaging and a neurological examination were planned.

Complete blood count (BC-60R VET; Mindray) was within normal limits. Serum biochemistry revealed a mild increase in total protein and creatine kinase levels, and a mild decrease in alanine aminotransferase activity (RX Monaco Analyzer; Randox Laboratories). A detailed biochemical analysis showed serum calcium and phosphorus concentrations within reference intervals (RIs), while ionised calcium and free thyroxine were slightly below their respective lower RIs. The solubility product was below the threshold for metastatic calcification. A low-dose dexamethasone suppression test (0.01 mg/kg dexamethasone IV at time 0) was performed, and serum cortisol concentrations were measured at 0, 4 and 8 h (Table 1). Parathyroid hormone and serum vitamin D concentrations were within the RI.

Table 1

Serum biochemistry and hormone analysis results of the patient

Parameters	RI	Patient
Thyroid-stimulating hormone (ng/ml)	0–0.38	0.04
Free thyroxine (ng/dl)	1–2.5	0.9
Parathyroid hormone (pmol/l)	0–40	0.15
Ionised calcium (mg/dl)	4.4–5.9	4.26
Serum calcium (mg/dl)	9.3–11.5	11
Serum magnesium (mg/dl)	1.58–2.16	2.1
Phosphorus (mg/dl)	2.5–6	6
Solubility product* (mg2/dl2)	<70	66
Low-dose dexamethasone suppression test (µg/dl)	†	3.3 (0 h)
		<1.5 (4 h)
		<1.0 (8 h)
Vitamin D (25-hydroxyvitamin D) (nmol/l)	65–170	80
Urinary total protein (mg/l)	100–500	456.7
Urinary creatinine (mg/dl)	100–500	371.7
Urine protein:creatinine ratio	‡	0.1

*

Solubility product (Ca × P <70 mg^2//dl ² )

†

In cats, an 8-h post-dexamethasone cortisol concentration <1.1 µg/dl is considered consistent with adequate suppression (hyperadrenocorticism unlikely). Values >1.4 µg/dl suggest adrenal-dependent hyperadrenocorticism, but pituitary-dependent hyperadrenocorticism cannot be excluded. Concentrations in the range of 1.1–1.4 µg/dl are considered inconclusive. Suppression at both 4 h and 8 h is indicative of a normal hypothalamic–pituitary–adrenal axis response

‡

Reference intervals (RIs): <0.5 = normal; 0.5–1.0 = borderline/suspicious; 1.0–5.0 = mild proteinuria/prerenal disease; 5.0–13.0 = mild-to-moderate proteinuria/prerenal disease; >13.0 = severe proteinuria. Animals with amyloidosis tend to present with the highest ratios

To determine the aetiology of the peripheral vestibular syndrome, open-mouth ventrodorsal bulla tympanica radiographs were obtained. The right bulla tympanica showed increased radiopacity, while the left appeared radiolucent and normal. Thoracic radiographs revealed numerous radiopaque masses of various sizes, most prominently in the bilateral axillary regions. In particular, the mediolateral projection of the right forelimb demonstrated a large, well-defined mass within the axillary area.

To confirm the diagnosis of otitis media and assess the masses, CT was performed under general anaesthesia. After premedication and induction, the cat was intubated and scanned using a Philips MX 16-slice CT unit (120 kV, 230 mAs, slice thickness 0.75 mm). The right bulla tympanica contained hypodense areas consistent with fluid accumulation, supporting a diagnosis of otitis media. No bone erosion or abnormal mineral density was detected (Figure 1a). Without recovery from anaesthesia, the patient underwent video-otoscopic examination. Using a 2.7 mm diameter, 0° rigid otoscope (MVM Medical), hyperaemia and inflammation of the right external ear canal were observed; the tympanic membrane was ruptured and inflammatory changes were evident within the middle ear. The findings were consistent with tympanic membrane rupture secondary to otitis externa and the subsequent development of otitis media. A sample was collected from the middle ear cavity for cytological evaluation during video-otoscopic examination. Giemsa-stained smears examined under oil immersion (× 100 objective) revealed a diffuse and dense population of coccoid bacterial organisms. In addition, multiple subcutaneous mineral-attenuating foci were observed in the dorsal thoracic region at the level of the T2–T3 vertebrae, along with a large, well-defined mineralised lesion in the right axillary region (Figure 1b).

Figure 1

Transverse CT images of the cat. (a) Right tympanic bulla filled with soft tissue attenuating material, consistent with otitis media (arrow). (b) Subcutaneous mineral-attenuating foci consistent with calcinosis cutis in the dorsal thoracic region between T2 and T3 vertebrae, and a large mineralised lesion in the right axillary region (arrows)

During the same anaesthetic episode, an excisional biopsy of the largest mass in the right axillary region was collected under aseptic conditions. The specimen was fixed in 10% neutral buffered formalin and submitted to the Department of Pathology, Faculty of Veterinary Medicine, Ondokuz Mayıs University for histopathological examination. The tissue was routinely processed through graded alcohols and xylene, embedded in paraffin wax, sectioned at 5 μm using a microtome, and stained with haematoxylin and eosin (Figure 2).

Figure 2

(a) Calcification of collagen fibrils (black X) surrounded by a hypocellular fibrous capsule (black arrow) (haematoxylin and eosin [H&E] × 200). (b) Calcification of collagen fibrils (black X), hypocellular fibrous capsule (black arrow) and inflammatory cell infiltrates (arrowhead) (H&E, × 200)

For the evaluation of possible metastatic calcinosis, the parathyroid glands, kidneys and adrenal glands were examined by ultrasonography using a Vetus 9 unit (Mindray); no abnormalities were detected. In addition, hyperadrenocorticism was ruled out by assessing serum cortisol levels, urinary cortisol:creatinine ratio and a low-dose dexamethasone suppression test. The patient’s history revealed no administration of vitamin D supplements, calcium injections, local trauma or prior surgical procedures; thus, iatrogenic and dystrophic calcinosis cutis aetiologies were excluded. Based on these findings, a diagnosis of multifocal subcutaneous idiopathic calcinosis cutis was established.

For the treatment of otitis media and management of neurological symptoms, the cat was prescribed cefixime (10 mg/kg PO q24h) and methylprednisolone (1 mg/kg PO q24h) for 14 days. The patient was monitored for 3 months. At follow-up, the head tilt persisted mildly, but ataxia, circling and nystagmus had completely resolved.

At the final examination, no new clinical signs were noted. The number and size of the subcutaneous masses remained unchanged, and the cat’s body condition score had improved. According to the owner, there were no signs of pain, and the overall health status was good. Continued periodic follow-up examinations were recommended.

Discussion

Reported cases of calcinosis cutis in cats range in age from 9 months to 13 years, with the majority being of metastatic origin, most commonly secondary to chronic kidney disease.^{3 –5,7 –11} Idiopathic forms account for approximately 17% of all reported calcinosis cutis cases.^{5,11 –13} In the present case, both otitis media and calcinosis cutis lesions were detected simultaneously; however, no causal relationship between the two conditions could be established. Theoretically, chronic inflammatory processes or a systemic inflammatory response could influence mineral metabolism; however, the biochemical data in this case indicated no disturbance in calcium–phosphorus balance. The calcinosis cutis lesions were incidentally identified during physical examination, and available evidence suggests that these two pathologies do not represent interdependent processes. There is no evidence in the literature to suggest that otitis media or secondary vestibular syndrome can trigger the development of calcinosis cutis.

Previously reported idiopathic calcinosis cutis lesions have been localised to the right flank, ¹¹ dorsal thoracolumbar ¹² and dorsal thoracic regions. ¹³ In the present case, the calcinosis cutis lesions were multifocal–differing from previous reports–yet clustered in the dorsal thoracic region. Although idiopathic calcinosis cutis in cats is most often described in the thoracic region, larger case series and epidemiological studies are needed to elucidate possible predispositions related to age, sex, neuter status and lesion localisation.

The histopathological findings in this case, including a fibrous capsule, lymphocyte–histiocyte-predominant infiltrates, multinucleated giant cell reaction and fat necrosis-associated calcification, are consistent with dystrophic calcification; however, similar histological appearances have been reported in idiopathic calcinosis cutis, and thus histology alone is not a gold standard for aetiological differentiation. In a large canine cohort, histopathological patterns, the composition of the inflammatory infiltrate and the degree of fibrosis showed no significant correlation with the underlying cause. ² In this case, although classified as idiopathic based on clinical and biochemical findings, a dystrophic mechanism cannot be entirely excluded, and the lesions may conceivably have developed at sites of prior unrecognised microtrauma, injections or subclinical panniculitis. Therefore, aetiological classification should be based on clinical and biochemical context.

The treatment of calcinosis cutis, as reported in the literature, depends on identification of the underlying cause and the clinical impact of the lesions. In metastatic or dystrophic forms, priority is given to treating the primary disease (eg, chronic kidney disease, hyperthyroidism, hypercalcaemia), whereas in idiopathic cases, surgical excision is often chosen for lesions causing symptomatic, cosmetic or functional problems.^5,11,14 Various medical and surgical treatment options for calcinosis cutis have been reported in the human literature, including surgical excision, warfarin, bisphosphonates, minocycline, diltiazem, aluminium hydroxide, probenecid, intralesional corticosteroids, intravenous immunoglobulin, carbon dioxide laser therapy and extracorporeal shock wave lithotripsy; ¹⁵ however, their efficacy and safety in cats remain to be investigated. In this case, surgical excision was not performed because of the multifocal distribution of the lesions. Follow-up examinations revealed no pain, movement limitation or lesion enlargement. Surgical intervention may be deferred as long as quality of life is unaffected; however, the patient should be monitored in the long term.

This case has several limitations. First, despite the multifocal nature of the lesions, only the largest mass was biopsied, with the assumption that other lesions shared the same histopathological features. This may introduce sampling bias and prevent definitive characterisation of all lesions. Second, special histochemical stains (eg, von Kossa, Alizarin Red) and mineral typing were not performed to confirm the presence and composition of calcium salts, limiting characterisation of the calcification. Third, potential differences in units/interpretation of the calcium–phosphorus product and ionised calcium, as well as biological variability (pre-analytical/analytical), may have influenced the results; single time-point measurements may be insufficient to completely rule out metastatic calcification risk. Fourth, the follow-up period was relatively short (3 months), and full-body cross-sectional imaging was not performed to assess the dynamic course of all lesions. In addition, biochemical analyses were not repeated during follow-up owing to the owner’s financial constraints, further limiting generalisable conclusions about long-term prognosis and lesion stability. Finally, in the concurrent otitis media, empirical treatment was initiated based on cytological examination instead of microbiological culture.

Conclusions

This case highlights the importance of considering idiopathic calcinosis cutis as a differential diagnosis in cats presenting with subcutaneous nodules, even when unrelated clinical problems are the primary reason for evaluation. Careful physical examination and histopathological confirmation remain essential for accurate diagnosis. Long-term monitoring is recommended, particularly in multifocal cases, to assess lesion stability and quality of life.