TL;DR: A firm lump between a cat's shoulder blades is often a reaction to a recent injection, but it should be evaluated by a veterinarian within 7 to 14 days to rule out serious conditions like malignancy.
What could a hard lump between my cat's shoulder blades be?
Finding a firm mass in this location is a common discovery for pet owners. Potential causes include:
- An injection-site granuloma (a common inflammatory reaction to a recent vaccination)
- A sebaceous cyst or lipoma (fatty tumor)
- An abscess resulting from a puncture wound
- Feline injection-site sarcoma (FISS), a rarer but more serious growth
Is a lump between my cat's shoulder blades considered a medical emergency?
- The urgency level is Low if the cat is acting normally and the lump is not painful, bleeding, or rapidly expanding.
- Stable lumps that are not causing distress do not require an immediate emergency room visit.
- Any new mass should be evaluated by a veterinarian during a scheduled appointment within the next 7 to 14 days to rule out malignancy.
How does taking a photo of the lump help with my cat's veterinary triage?
- Allows the veterinary team to monitor the lump's progression and growth rate over time.
- Helps the triage nurse identify skin changes such as discoloration, ulceration, or hair loss.
- Provides critical information that helps your vet determine how quickly your cat needs to be seen.
Clinical Context (Merck Veterinary Manual)
In cats, a hard lump on the back between the shoulders may be indicative of vaccine-induced fibrosarcoma, which appears as a nodule or plaque in the soft tissues. These tumors are associated with rabies and feline leukemia virus vaccinations, where aluminum hydroxide (a common adjuvant) may trigger fibroblast proliferation leading to neoplastic transformation. While lymphoma is the most common spinal neoplasia in cats, fibrosarcomas should be considered in the differential diagnosis for masses in this region. Diagnosis of spinal neoplasia relies on radiography, myelography, CT or MRI, and surgical biopsy.
Chapter: Neurology, Oncology
Source: The Merck Veterinary Manual, 11th Edition (Page 1275)