Small Animal Dermatology, 3rd edition

386 DISEASES/DISORDERS

 Reactive cutaneous histiocytosis:
Formalin fixed tissue: CD18+, MHC class II+, CD90(Thy-1)+, E-cadherin-
Frozen section: CD1a+, CD11c+, CD4+, CD90(Thy-1)+.

 Reactive systemic histiocytosis:
Formalin fixed tissue: CD18+, MHC class II+, CD90(Thy1)+
Frozen: CD1a+, CD11c+, CD4+, CD3+
Enzyme markers: TCR alpha and and beta+, acid phosphatase, lysozyme (cr-1-

antitrypsin)+.

 Histiocytic sarcoma:
Formalin fixed tissue: CD18+, CD204+, MHC class II+
Frozen section: CD1a+, CD11c+.

THERAPEUTICS

 Histiocytoma:
Observation without treatment; most nodules will resolve within 3 months
Nodules often appear more inflamed, crusted, or scabbed during involution (see

Figure 25.10)

Excisional biopsy is curative

Multiple tumors: may respond to prednisolone 1 mg/kg PO q24h; tapered until

lesions resolve

Pruritic nodules may respond to the topical application of corticosteroids in

DMSO.

 Reactive cutaneous histiocytosis:
50% respond to corticosteroids
Prednisolone 1 mg/kg PO q24h tapering dosage; treatment lasting from 4 to

18 months

Spontaneous remission can occur

Cycline antibiotics: tetracycline (250 mg PO q8h for dogs<10 kg; 500 mg PO

TID dogs>10 kg); doxycycline (10 mg/kg PO q24h); minocycline (5 mg/kg PO

BID); often administered with niacinamide 250 mg PO for dogs<10 kg and

500 mg PO for dogs>10 kg

Cyclosporine: 5–10 mg/kg PO q24h; dose may be tapered slowly over time; main-

tenance therapy usually necessary; liver enzymes must be monitored for hepa-

totoxicity; vomiting is the most common side effect

Alternatives: vitamin E, essential fatty acids.

 Reactive systemic histiocytosis:
Cyclosporine: 5–10 mg/kg PO q24h; dose may be tapered slowly over time; main-

tenance therapy usually necessary; liver enzymes must be monitored for hepa-

totoxicity; vomiting is the most common side effect

Leflunomide: 2–4 mg/kg PO q24h; trough levels of 20 mg/mL may be opti-

mum; variability in drug metabolism, trough levels must be monitored;