Approach to skin nodules and nodular dermatitis

Define nodule

A circumscribed solid elevation greater than 1cm in diameter and usually extends into deeper layers of skin

What do nodules usually result from?

• Inflammatory cells

• Neoplastic cells

• Deposition of fibrin or crystals (e.g.- calcinosis cutis)

What are some ddx of nodules?

How can you describe the clinical presentation of a nodule?

• Location

• Number

• Size

• Behaviour (acute vs gradual)

• Aspect/clinical features

  • Warm and/or painful

  • Hard, soft, elastic, fluctuant, movable, fixed

  • Alopecic, smooth/rough surface

  • Ulcerated (possible presence of draining tracts)

  • Hyper/hypopigmented

How can you diagnose the cause of an nodule?

Cytology

• FNA

• Apposition (if ulcerated/dischargin)

Will either be diagnostic or direct you to further testing (culture, special stains, immunocytochemistry)

What steps may you take after cytological testing for a nodule?

Histology

• Excision of whole nodule

• Punch/wedge biopsy

Depends on clinical presentation

(aseptic collection of sample for culture)

What further diagnostic tests can be done on nodules?

• Immunohistochemistry

• Special stains

• PCR

• Biochem, urinalysis (e.g.- calcinosis cutis)

• Serology (e.g. Leishmania, Toxoplasma, Neospora, Cryptococcus)

What are some common causes of foreign body reaction leading to nodules?

• Plant material

• Grass awns

• Embedded insect mouth parts

• Suture material

• Porcupine quills

Endogenous: e.g.-

• hair, sebum, keratin

• Calcium salt

• Tyrosine salt

What commonly causes an infectious nodule?

Abscesses

Penetrating wounds, bites, foreign bodies

Proliferation of bacteria involved

• Dog: Staphylococcus

• Cat: Polymicrobial

  • Pasteurella, Staph, Strep

When you have nodules on the face in cats what should you consider?

• Rodent bites so Mycobacteria and Poxvirus (more ulcerative than nodular)

What filamentous bacteria can cause nodules?

• Actinomyces

• Nocardia

• Actinobacillus

What are the clinical signs of a nodule caused by filamentous bacteria?

• Nodules and abcesses with ulcers, draining tracts and cellulitis

• Anywhere in body usually from bite wounds or penetrating foreign bodies

• Serosanguineous exudate

• Possible systemic signs

How are nodules caused by filamentous bacteria diagnosed?

• Cytology (gram, ZN stain)

  

• Histology

• Culture

• Molecular technique (PCR, gene sequencing, MALDI-TOF)

How are nodules caused by filamentous bacteria treated?

• Surgical drainage and antimicrobial therapy

• Long courses

What are the two main presentations of a nodule caused by mycobacteria (saprophytic)?

• Dog: Canine leproid granuloma (Short coated breeds, boxers ++)

• Cat: Feline leprosy syndrome (++Outdoor male cats)

What are the clinical signs of a mycobacteria nodule?

• Single or multiple, firm, well-circumscribed nodule in skin or subcutis

  • Peripheral lymphadenomegaly

• CLG usually self-limiting

• FLS progressive and occasionally aggressive clinical course

(extremely fastidious and generally uncultivable)

How is a mycobacteria nodule diagnosed?

• Cytology

• Histology

• Culture- generally uncultivable, needs specialist mycobacterial culture and subsequent genotyping at lab

• PCR

How are CLG and FLS treated?

• CLG- spontaenous regression in 1-3 months, can persist in immunocompromised

• FLS- progressive, empirical combination of 2/3 antibiotics, surgical excision but possible recurrence

  • Long courses in some cases life long

What atypical/non tuberculous mycobacteria can cause nodules?

M. avium complex

M. fortuitum

M. thermoresistible

(Penetrating wounds in cats> dogs)

What are the clinical signs of nodules caused by atypical/ non tuberculous mycobacteria?

• Granulomatous panniculitis: single/ multiple nodules, plaques, macules and diffuse swelling- multiple punctate ulcers and draining tracts

  • Pyogranulomatous lobular pneumonia

  • Disseminated systemic disease

How are atypical/ non tuberculous mycobacteria treated?

Empirical antibiotic treatment +/- surgical intervention

What is the main source of M tuberculosis mycobacteria causing nodules?

• Mainly from infected wild rodents

  • Cats>dogs

(M.microti, M.bovis, M.tuberculosis)

What are the clinical signs of a nodule caused by M. tuberculosis?

• Male outdoor cats- face, extremities, tail base, perineum

• Firm nodules, ulcerations, non-healing wounds with draining tracts-> thick yellow to green fluid and systemic signs

• Localised or generalised lymphadenopathy

How is a nodule caused by M. tuberculosis diagnosed?

• Cytology

• Histology

• Culture- specialist and subsequent genotyping at lab

• PCR

How is a nodule caused by M. tuberculosis treated?

• Notifiable disease- owner might need to be screened at TB clinic

• Euthanasia/ empirical multidrug regimens

What are the types of nodules caused by dermatophytes? What aetiological agents cause them?

• Dermatophytic pseudomycetoma (Cats- persian and DLH+)

  • M. canis

• Nodular dermatophytosis (Dogs)

  • M gypseum, T. mentagrophytes, M. canis

How does Dermatophytic pseudomycetoma present?

• Deep dermal and or subcut infection

• Painless, single or multifocal ulcerated dermal nodules, yellow granular discharge

• No history of skin trauma

• Neck, dorsum, tail, flanks or limbs

How is Dermatophytic pseudomycetoma diagnosed and treated?

D: cytology, histopath, culture from exudate or FNA

T: systemic antifungals (itraconazole, ketoconazole, terbinafine) +/- surgery

How does Nodular dermatophytosis present?

• Single lesion commonly

• Or multiple erythematous, alopecic, exudative nodules

• On head, neck, limbs

How is Nodular dermatophytosis diagnosed and treated?

• D: cytology, histopath, culture from exudate or fresh tissue

• T: systemic antifungal (itroconazole, ketoconazole)

How do fungal subcutaneous nodules present?

• Traumatic implant of saprophytic organisms on soil and vegetation

  • Significant tissue destruction and inflammation

• Chronic and localised to disseminated in immunocompromised

How are subcutaneous fungal nodules diagnosed and trated?

• D: cytology, histopath, fungal culture, PCR, Serology (important for cryptococcus)

• T: Ideally based on culture, azoles main systemic antifungal, amphotericin B, terbinafine

What are some differnt types of fungal subcutaneous nodules?

• Mycetomas- pyogranulomatous nodules that contain tissue grains or granules colonies of organisms and necrotic debris

  • Pigmented fungi

  • Unpigmented fungi composed of dense

• Chromomycosis- subcutaneous and systemic disease associated with pigmented fungal elements

  • pigmented hyphal elements but NOT grains in tissues

• Hyalohyphomycosis

  • Unpigmented

• Cryptococcosis

  • In the environment (soil, trees, bird droppings)

  • Most common systemic

• Sporotrichosis mycosis in cats

  • Emerging zoonotic disease – mainly in Latin America (tropical/subtropical climates) but spreading

  • Hunting dogs, outdoor cats ++

What protozoa can cause nodular skin lesion?

• Toxoplasma gondii

• Neospora caninum

  

• Leishmania spp

All rare

How can nodules due to protozoa be diagnosed?

• Cytology

• Histopath + IHC + PCR +/- DNA sequencing (distinction Toxo/Neospora can be challenging)

• Serology

What parasite can cause nodular skin lesions?

Dirofilaria repens

• Transmitted by mosquitoes

How can nodules due to parasites be diagnosed?

• FNA can show microfilariae

• Ultrasound evaluation

• Histopathology

What immune mediated conditions can cause nodules?

• (Juvenile) Sterile granulomatous dermatitis and lympadenitis

• Sterile pyogranulomatous dermatitis and panniculitis

• Eosinophilic granuloma

What are the two main types of histiocytic proliferative disorders?

• Neoplastic

  • Histiocytomas (solitary lesions)

  • Canine cutaneous langerhans cell histiocytosis (multiple histiocytomas)

  • Histiocytic sarcoma

  • Feline progressive histiocytosis

• Reactive

  • Cutaneous histiocytosis (inflammatory lymphohistiocytic proliferative disorder that primarily involves skin and subcutis)

  • Systemic histiocytosis (generalized histiocytic proliferative disease)

    

How does cutaneous histiocytosis present grossly?

• multiple cutaneous and subcutaneous nodules up to 4 cm diameter – non-painful, non-pruritic

• skin ulceration common

• may disappear spontaneously or regress and appear at new sites simultaneously

• face, nose, neck, trunk, extremities (including foot pads), perineum, and scrotum

How does systemic histiocytosis present grossly?

• involves skin, ocular and nasal mucosae, and peripheral lymph nodes

• lung, liver, bone marrow, spleen, peripheral and visceral lymph nodes, kidneys, testes, orbital tissues, nasal mucosa

How are reactive histiocytic proliferative disorders diagnosed?

histopath + IHC

How are reactive histiocytic proliferative disorders treated?

• Glucocorticoids, ciclosporin