A 15-year-old castrated male domestic shorthair cat presented with a 2-month history of progressive lameness, swelling, and pain in its right front paw.
History
The patient was an indoor only cat. No other animals in the household were showing clinical signs. He was anorectic and had vomited a few times after eating in the recent past.
The previous attending veterinarian had taken radiographs of the affected paw and conducted a basic serum biochemical profile; however, results were not definitive. Therapy for the pain and lameness, including butorphanol, was administered, and the patient received a vitamin and mineral supplement (Lixotinic, zoetisus.com). No apparent changes in the patient’s condition were noted while receiving these treatments.
Physical Examination
On initial physical examination, the patient appeared depressed and painful. He was hesitant to bear weight on the affected limb, and sedation (acepromazine, 0.02 mg/kg IM, and hydromorphone, 0.075 mg/kg IM) was required to perform a full physical examination.
Upon closer examination, the cat’s right front paw demonstrated severe inflammation, and a bloody, purulent discharge was present between the footpads and interdigitally. All of the nail beds varied from eroded to ulcerated (Figure 1).
In addition, a small cranial abdominal mass was palpated, and a mild heart murmur was auscultated. The patient also had moderate dental disease. The remainder of the examination was normal.
Figure 1. Ulceration of the nail fold (A); all digits were affected. A bloody, purulent discharge was associated with the areas of ulceration (B).
Diagnostics
Laboratory Analysis
Complete blood count (CBC), serum biochemical profile, and urine analysis were conducted by the in-house laboratory.
- CBC showed a mild nonregenerative anemia, neutrophilia with left shift, and mild lymphopenia, suggesting inflammation and stress.
- Serum biochemical profile revealed increased blood urea nitrogen (37 mg/dL; reference range, 18–32), decreased potassium (2.9 mEq/L; reference range, 3.2–4.5), and decreased calcium (8.4 mg/dL; reference range, 8.8–11).
- Urinalysis values were within normal limits.
Imaging
Radiographs of the thorax and right forelimb were performed under sedation. Thoracic radiographs revealed a solitary 2.9 cm (height) mass in the left caudal lung lobe (Figure 2). Right forelimb radiographs suggested bone lysis of the P3 of digits 1 and 2.
FIGURE 2. This lateral radiograph shows an approximately 2.9 cm (height) soft tissue mass most likely residing in the left caudal lung lobe.
Skin Cytology
Skin samples from the ulcerated areas of the nail beds were collected by scraping the surface of the skin with a scalp blade and then were stained with Diff-Quik for cytologic evaluation. Bacterial rods and cocci were visualized. Neutrophilic inflammation and multinucleated epithelial cells were also present.
Skin Pathology
The skin samples were submitted to a clinical pathologist for analysis. Large clusters of neoplastic epithelial cells were noted, as well as many inflammatory leukocytes, rods, and cocci. The pathologist’s diagnosis was carcinoma, chronic neutrophilic inflammation, and bacterial infection. The owner declined further diagnostics for the abdominal mass.
Diagnosis
Initial Diagnosis
Combined with radiographic evidence, primary pulmonary carcinoma with metastasis to the digits of the right front foot and bacterial infection were tentatively diagnosed.
Definitive Diagnosis
Due to the presence of a mass in the lung and the lysis of the digits, the final diagnosis was primary bronchial carcinoma with metastasis to the digits, also known as lung-digit syndrome.
Cats with pulmonary neoplasia commonly have a history of increased lethargy, depression, anorexia, diarrhea, and vomiting.1 Our patient showed signs of systemic disease, including anorexia, depression, digital pain, and lameness.
However, of all cats with pulmonary neoplasia, only 25% to 50% present with respiratory signs over the course of their disease.2,3 Since this patient did not show respiratory signs, he fit well into the defined clinical picture of primary metastatic bronchial adenocarcinoma.
Although little information is available, metastasis of a pulmonary neoplasm to the digits appears to be rare. In one report of 116 cases of feline primary pulmonary neoplasia, only one case had digital involvement.4 Much like our patient, the most common presenting complaint for cats with metastasis to the digits is lameness and pain associated with one or more limbs.
Differential Diagnosis
The differential diagnosis for the skin lesions in this cat includes neoplasia, infectious paronychia (bacterial or fungal), and immune-mediated disease.5
Therapeutic Options
Prognosis for cats with metastasis of primary pulmonary carcinoma to the digits is generally grave. Advanced age may contribute to this shorter survival time, but treatment options are limited. A recent retrospective study of 36 cats with this condition found mean survival time to be 58 days (median, 64 days), with a range of 2 to 122 days.4
In this case, we did not attempt treatment, and the owners opted for euthanasia due to short survival time associated with current available treatments and poor quality of life of the patient. Palliative care would have consisted of pain control and treatment of the secondary infections.
Amputation
For those with digit metastasis, digital amputation as a treatment option has limited benefit; the median disease-free interval in cats with and without evidence of a lung mass at time of amputation was found to be 24 days, with median post amputation survival time being 104 days.6
Tumor Removal
An older retrospective study showed that surgical removal of primary lung tumors resulted in a median survival time of 115 days (range, 13–1526 days).7 Median survival times were 698 days for cats with moderately differentiated tumors, and 75 days for cats with poorly differentiated tumors. However, the survival times did not take into account the presence or absence of metastatic disease at time of surgery.
In a more recent study, signs, such as dyspnea and pleural effusion, as well as evidence of metastasis, were shown to be associated with significantly lower survival times.2
Chemotherapy
Limited studies have evaluated the use of chemotherapy in cats with evidence of primary pulmonary neoplasia and metastatic disease. One case report documents management of a single cat that had a well differentiated pulmonary carcinoma and no evidence of metastatic lesions, using lobe resection and adjuvant therapy with mitoxantrone.8
Profile: Primary Pulmonary Neoplasia
Prevalence
Primary pulmonary neoplasia is most common in older cats, with 11 to 12 years the mean age of presentation;2 however, it is a rare occurrence in cats.
Previous reports have suggested that it occurs in only 2.2 per 100,000 cats, but these numbers may be rising. This increase in occurrence may be due to increased age of the feline population or increased exposure to atmospheric pollutants.5,9 Another possibility is that, with the use of more advanced technology and increased owner awareness about their cats’ health, we are able to diagnose this condition more accurately.
Classification
There are several types of primary pulmonary carcinoma in cats, with the most common being bronchial adenocarcinoma (66%), followed by anaplastic carcinoma (12%), bronchoalveolar carcinoma (10%), and bronchial adenosquamous carcinoma (8%).10 Both bronchial adenocarcinoma and bronchoalveolar carcinoma have been associated with metastasis to the digits, a condition also known as lung-digit syndrome.5
Metastasis
Primary pulmonary carcinomas have been shown to metastasize to the digits, ulna, fundus, lymph nodes, kidneys, spleen, limb muscles, and intestinal wall.11-13 The pathogenesis of pulmonary carcinoma’s predilection for digit metastasis is currently unknown, but it has been hypothesized that the digits are selectively affected due to the high digital blood flow in cats, which allows cats to maintain an appropriate core temperature. In patients with pulmonary carcinoma, this increased blood flow may predispose the digits to metastatic embolization and, thus, metastatic disease.5 Metastasis is most commonly found in weight-bearing digits.13
Presentation
Cats with metastatic bronchial adenocarcinoma do not usually present for primary respiratory disease. Initial complaints are commonly lameness and pain associated with digital metastasis, or visual or neurologic deficits associated with metastasis to the fundus or brain.4,12 Dyspnea, tachypnea, and cough can signify pulmonary involvement, while auscultation of the lungs may reveal increased bronchovesicular sounds or dullness of respiratory sounds. A history of anorexia and lethargy can also be an indication of neoplasia in older cats.
Diagnostics
- Thoracic radiographs reveal the presence of one or more pulmonary masses.
- Pleural effusion is common in cats with advanced pulmonary neoplasia, and thoracocentesis may confirm the diagnosis when carcinoma cells are found in pleural fluid.
- Fine needle aspiration (FNA) of pulmonary masses, using ultrasound or computed tomography guidance, is often diagnostic.
- Bronchoalveolar lavage and transtracheal wash are additional diagnostic options.14
- Biopsy of the affected digit(s) may allow histopathologic confirmation of the diagnosis. Samples collected by FNA or skin surface cytology are less invasive, and may help with the diagnosis; however, they may not provide sufficient information to confirm a diagnosis.
- The gold standard for histopathologic evaluation is full digit amputation.7
Summary
- Primary metastatic bronchial carcinomas can be difficult to diagnose and may present with lameness as a primary complaint, as opposed to respiratory signs.
- Consider lung-digit syndrome as a possible differential diagnosis for an older cat presenting for progressive single or multiple limb pododermatitis and lameness.
- Difficulties of treatment and prognosis should be considered during management.
- The majority of cats diagnosed with metastatic primary pulmonary adenocarcinoma are euthanized due to continued lameness or nonspecific signs of disease, including anorexia, depression, and lethargy.
CBC = complete blood count; FNA = fine needle aspiration
References
- Goldfinch DN, Argyle DJ. Feline lung-digit syndrome: Unusual metastatic patterns of primary lung tumours in cats. J Feline Med Surg 2012; 14(3):202-208.
- Maritato KC, Schertel ER, Kennedy SC, et al. Outcome and prognostic indicators in 20 cats with surgically treated primary lung tumors. J Feline Med Surg 2014; 16(12):979-984 [epub ahead of print].
- Mehlhaff CJ, Mooney S. Primary pulmonary neoplasia in the dog and cat. Vet Clin North Am Small Anim Pract 1985; 15(5):1061-1067.
- Gottfried SD, Popovitch CA, Goldschmidt MH, Schelling C. Metastatic digital carcinoma in the cat: A retrospective study of 36 cats (1992-1998). JAAHA 2000; 36(6):501-509.
- Goldfinch DN, Argyle DJ. Treatment of a well differentiated pulmonary adenocarcinoma in a cat by pneumonectomy and adjuvant mitoxantrone chemotherapy. J Feline Med Surg 2012; 6:199-205.
- Wobeser BK, Kidney BA, Power BE, et al. Diagnoses and clinical outcomes associated with surgically amputated feline digits submitted to multiple veterinary diagnostic laboratories. Vet Pathol 2007; 44(3):362-365.
- Hahn KA, McEntee MF. Prognosis factors for survival in cats after removal of a primary lung tumor: 21 cases (1979-1994). Vet Surg 1998; 27(4):307-311.
- Clements DN, Hogan AM, Cave TA. Treatment of a well differentiated pulmonary adenocarcinoma in a cat by pneumonectomy and adjuvant mitoxantrone chemotherapy. J Feline Med Surg 2004; 6(3):199-205.
- Barr F, Gruffydd-Jones TJ, Brown PJ, Gibbes C. Primary lung tumors in the cat. J Small Anim Prac 1987; 28:1115-1125.
- Hahn KA, McEntee MF. Primary lung tumors in cats: 86 cases (1979-1994). JAVMA 1997; 211(10):1257-1260.
- Salguero R, Langley-Hobbes S, Warland J, Brearly M. Metastatic carcinoma in the ulna of a cat secondary to a suspected pulmonary tumour. J Feline Med Surg 2012; 14(6):432-435.
- Sandmeyer LS, Cosford K, Grhn BH. Metastatic carcinoma in a cat. Can Vet J 2012; 50(1):95-96.
- Scott-Moncrieff JC, Elliott GS, Radovsky A, Blevins WE. Pulmonary squamous cell carcinoma with multiple digital metastases in a cat. J Sm Anim Pract 1989; 30:696-699.
- Withrow SJ, Vail DM, Page R (eds): Withrow and MacEwen’s Small Animal Clinical Oncology, 5th ed. Philadelphia: Saunders, 2012, p 120.