Skin: deep folliculitis and furunculosis

Introduction

• Cause : follicular infection that breaks through hair follicle → furunculosis.
• Begins as surface or follicular infection (bacterial, fungal or parasitic).
• Signs : vary from discrete papular lesions to poorly demarcated areas of alopecia, tissue swelling and inflammation.
• Certain types clinically distinctive entities, eg canine acne , pododermatitis and furunculosis , idiopathic furunculosis of German Shepherd Dog , pyotraumatic folliculitis , callus dermatitis.
• Diagnosis : signs, histopathology.
• Treatment : antibiotics.
• Prognosis : good with treatment.

Diagnosis

Clinical signs

• Pustules centered around hair follicle as in superficial folliculitis but larger in size.
• Erythematous bases of pustules may be present as firm nodules.
• Few infected follicles → discrete papular lesions.
• Many infected follicles → alopecia, tissue swelling and inflammation.
• Papules → pustules → hemorrhagic bullae, edematous plaques and nodules → ulceration +/- fistulae → hemorrhagic crust +/- necrosis.
• Hyperpigmentation and lichenification occur with chronicity.
• Regional or generalized lympadenopathy.
• On palpation deep involvement is obvious, see pyotraumatic dermatitis.

• Pus from pustules or fistulas may become pink or red indicating severe dermal damage.
• Large dark red-violet lesions indicate deeper infection than smaller pinkish lesions.
• Hemorrhagic bullae are a distinctive clinical feature in some dogs.

• May be difficult to distinguish from pyotraumatic dermatitis .
• Pyrexia.

Diagnosis

Differential diagnosis

• Deep pyoderma .
• Neoplasia, especially severe malignancy of mammary region .
• Pyotraumatic dermatitis especially on face, eg Rottweiler, Golden Retriever.
• Foreign body reaction.

Sequelae

Prognosis

• Good if predisposing factors treated.
• Bacteremia and sepsis are uncommon sequelae.
• Hair will not grow in scarred areas.

Expected response to treatment

• Regression of clinical signs, usually within 4-12 weeks.

Reasons for treatment failure

• Failure to identify and treat underlying cause.
• Inadequate dose or duration of antibiotic therapy.

Sources

Publications

Refereed papers

• Scott D W et al(1998) Efficacy of clindamycin hydrochloride capsules for the treatment of deep pyoderma due to Staphyloccus intermedius infection in dogs. Can Vet J 39 (12), 753-756.
• Krick S A & Scott D W (1989) Bacterial folliculitis, furunculosis and cellulitis in the GSD - a retrospective analysis of 17 cases. JAAHA 25 , 23-30.