Approach to skin nodules

what is a nodule?

a circumscribed solid elevation greater than 1cm in diameter that usually extends deeper layers of skin

what doe nodules usually result from?

infiltration of inflammatory cells, neoplastic cells or deposition of fibrin or crystals

what are the noninfectious differentials for nodules?

• foreign body (plant / inorganic material —> calcinosis)

• inflammatory (eosinophilic granuloma)

• cutaneous drug eruption or injection reaction

• sterile pyogranulomatous dermatitis and panniculitis

• juvenile cellulitis

• histiocytosis

what features of the clinical presentation of nodules should we consider?

• location on the body

• number (single vs multiple)

• size

• behaviour (acute vs gradual onset)

• aspect / clinical features

  • warm or painful

  • hard, soft, elastic, moveable, fixed, etc.

  • alopecic, smooth or rough

  • ulcerated

  • hyper/hpopigmented

what cytology should we perform for nodules?

• fine needle aspirate

• apposition (if ulcerated or discharging)

what histology could we perform for nodules?

• excision of whole nodule

• punch / wedge biopsy

• choice of histology depends on clinical presentation (number, size, location)

what diagnostic tests could we perform for nodules?

• cytology

• histology

• immunohistochemistry, clonality

• special stains (gram, PAS, ZN, GMS)

• PCR

• biochemistry, urinalysis (calcinosis cutis)

• serology (e.g. Lesihmania, Toxoplasma, Neospora, cryptococcus)

what foreign body reaction may cause nodules?

• plant material

• grass awns

• embedded insect mouth parts

• suture material

• procupine quills

• endogenous material - hair, sebum, keratin, calcium salt, tyrosine crystals

what bacteria is usually seen in dogs with abscesses?

staphylococcus

what bacteria is usually seen in cats with abscesses?

polymicrobial anaerobic infections from bite wounds (Bacterioides, Fusobacterium)

what are possible filamentous bacteria causing infectious nodules?

• Actinomyces - oral / GI tract commensal

• Nocardia - cosmopolitan, soil saprophyte

• Actinobacillus - commensal organism in oral cavity

what are the clinical signs of filamentous bacteria?

• nodules and abscesses with ulcers, draining tracts and cellulitis

  • anywhere the bacteria are inoculated from bite wounds or penetrating foreign bodies

• serosanguineous exudate

• systemic signs - pyrexia, depression

  • with Nocardia - occasional systemic dissemination and pneumonia

how do we diagnose filamentous bacteria?

• cytology (may need to use special stains - Gram, ZN)

• histology (may need special stains) - see nodular to diffuse pyogranulomatous dermatitis and panniculitis, possibly with tissue grains ‘sulfur granules’

• culture

• molecular techniques - PCR, gene sequencing, MALDI-TOF

what is the treatment for filamentous bacteria?

surgical drainage and antimicrobial therapy

what does this Ziehl Neelsen stain FNA of a nodule show?