The Cat with Nodules

Table 2-11. Differential Diagnoses, Commonly Affected Sites, and Recommended Diagnostic Tests in a Cat with Nodules

Disease

Commonly Affected Sites

Treatment

Prognosis

Neoplasia*

Varies with individual neoplastic diseases

Surgical excision and/or tumor specific therapy

Poor to excellent depending on the individual tumor.

Abscesses (caused by bite wounds or foreign bodies)

Fluctuating nodules most commonly around neck, shoulders, and tail base

Surgical drainage, antibacterial treatment

Good

Opportunistic mycobacterial infection* (ubiquitous, facultatively pathogenic organisms such as Mycobacteria fortuitum, M. chelonei, M. smegmatis, cause lesions after traumatic implantation into subcutaneous tissue)

Nonhealing ulcerated nodules with draining tracts predominantly in the abdominal or inguinal area (Fig. 2-58and Fig.2-59).

Wide surgical excision followed by combination antimicrobial therapy

Fair with appropriate surgical approach

Cryptococcosis* (uncommon infection of sometimes immunocompromised host with ubiquitous, saprophytic, yeast-like fungus Cryptococcus neoformans)

Upper respiratory, cutaneous, central nervous system, and ocular signs. Firm swelling over the bridge of the nose (Fig. 2-60), papules, nodules, ulcers and draining tracts. Nose, lips, and claw beds may be affected.

Antimycotic therapy with azoles and/or amphotericin B

Fair

Bacterial pseudomycetoma (nonbranching bacteria such as coagulase-positive Staphylococciimplanted by trauma form grains of compact colonies surrounded by pyogranulomatous inflammation; rare disease)

Firm nodules with draining fistulae (Fig. 2-61)

Complete surgical excision, postsurgical antibacterial treatment

Fair with complete excision; guarded, if this is not possible.

Eumycotic mycetoma (ubiquitous soil saprophytes cause disease through wound contamination; rare disease)

Nodules with draining tracts and scar tissue. Grains vary in size, shape, and color.

Wide surgical excision followed by antimycotic therapy based on in vitro susceptibility testing.

Fair to guarded depending on surgical excision.

Feline Leprosy* (presumably transmission of an incompletely characterized mycobacterium that is difficult to culture through bite wounds from rats; rare disease in veterinary dermatology)

Single or multiple, nonpainful and nonpruritic nodules on head and limbs; sometimes ulcers and fistulae are present (Fig. 2-62a and Fig. 2-62b)

Surgical excision, combination antibiotic therapy

Fair

Actinobacillosis* (Oral commensal aerobic Actinobacillus ligneriesii is traumatically implanted, often through bite wounds; rare disease in veterinary dermatology)

Thick-walled abscesses of the head, mouth, and limbs discharging thick pus with soft yellow granules.

Surgical excision or drainage and long-term antibacterial therapy with streptomycin, chloramphenicol, sodium iodide or tetracyclines

Guarded

Histoplasmosis (uncommon infection with dimorphic, saprophytic soil fungus Histoplasma capsulatum; very rare disease in veterinary dermatology)

Papules, nodules, ulcers, and draining tracts with concurrent anorexia, weight loss, and fever; dyspnea and ocular disease

Antimycotic therapy with azoles, possibly in combination with amphotericin B

Guarded to grave

Nocardiosis* (Nocardia spp. are soil saprophytes that cause respiratory, cutaneous, or disseminated infections; very rare disease in veterinary dermatology)

Ulcerated nodules and abscesses, often with draining tracts, on the limbs and ventral abdomen

Surgical drainage, antibacterial therapy based on in vitrosusceptibility testing.

Guarded

Phaeohyphomycosis* (wound contamination by ubiquitous saprophytic fungi with pigmented hyphae; very rare disease in veterinary dermatology

Often solitary subcutaneous nodules on nose, trunk, or extremities

Wide surgical excision followed by antimycotic therapy based on in vitro susceptibility testing.

Guarded

Plague (infection with Yersinia pestisby inhalation of organism or through wound contamination or flea bites; very rare disease in veterinary dermatology)

Zoonosis: Spread through transmission of infected fleas, presentation of infected killed rodents, or direct infection!

High fever, depression, anorexia, and abscesses typically on the face or limbs in the bubonic form. Septicemic and pneumonic forms also exist.

Flea control, draining of abscesses, antibacterial therapy with tetracycline, streptomycin, or chloramphenicol

Fair, if recognized and treated promptly.

Sporotrichosis* (caused by ubiquitous dimorphic fungal saprophyte Sporothrix schenkii that infects wounds; uncommon disease in veterinary dermatology)

Zoonosis: Transmission to humans through contact with an ulcerated wound easily possible!

Multiple nodules or ulcerated plaques on the head, distal limbs, tailbase (Fig. 2-63). Anorexia, lethargy, fever, and depression possible concurrently

Antimycotic therapy with iodides or azoles

Fair

Sterile granulomatous and pyogranulomatous disease (unknown pathogenesis)

Firm, painless, nonpruritic dermal papules, plaques, and nodules typically on head and pinnae

Doxycycline / Niacinamide, immunosuppressive therapy, may resolve spontaneously

Fair

Sterile panniculitis (unknown pathogenesis)

Solitary nodules on ventral rump

Surgical excision

Good

Tuberculosis* (very rare in small animal dermatology; predominantly respiratory and digestive lesions)

Insidious ulcers, plaques, and nodules on head, neck, and limbs discharging yellow-green pus with unpleasant odor

Combination antimicrobial therapy, frequent euthanasia (public health concerns)

Poor