Page 1504 - Clinical Small Animal Internal Medicine

1442 Section 12 Skin and Ear Diseases

granuloma and pyogranuloma syndrome, multiple
VetBooks.ir cutaneous histiocytomas, and cutaneous lymphoma.
Immunohistochemistry may be required to differentiate
cutaneous histiocytosis from these conditions.
It is recommended to contact veterinary diagnostic
laboratories for availability and tissue submission
requirements for immunohistochemistry. Because a lim-
ited number of markers are available to be used on for-
malin fixed specimens, the submission of fresh tissue
samples may be necessary. Canine cutaneous histiocyto-
sis has been characterized by proliferation of CD1+,
CD11c+, MHC II +, CD4+, and Thy‐1+ (CD90) activated
dermal dendritic cells.

Therapy
Immunosuppressive drugs have been used with mixed
results. Most cases respond completely or partially to
immunosuppressive therapy with glucocorticoids, but
require long‐term or intermittent therapy to induce
Figure 164.1 Two‐year old Bernese mountain dog with remission and prevent reoccurrence. Up to 50% of cases
cutaneous histiocytosis. Nodular lesions are present on the lips respond to prednisone as sole therapy. Azathioprine,
and planum nasale.
ciclosporin, and leflunomide have also been shown to be
effective, and can be helpful in cases not responding to
glucocorticoid therapy. Tetracycline/niacinamide treat-
ment has been found to be effective as maintenance ther-
apy to avoid recurrence. Since tetracycline has been
unavailable in the US market, doxycycline or minocy-
cline can be substituted for tetracycline.

Prognosis
Prognosis is guarded. Up to one‐third of patients have
reoccurrence of skin lesions and thus long‐term therapy
is required. Dogs with nasal involvement may be more
likely to have recurrence.

Systemic Histiocytosis
Systemic histiocytosis is considered a disseminated form
of cutaneous histiocytosis. In addition to the skin and
mucocutaneous junctions, lesions may be found in the
lungs, spleen, liver, lymph nodes, eyelids, sclera, and
bone marrow.

Figure 164.2 Close‐up of the lesions on the lips of the dog in Etiology/Pathophysiology
Figure 164.1. Note the multiple, crusted, erosive to ulcerative The etiology and pathogenesis of SH are currently
nodules. unknown. As for CH, since infectious agents have not
been identified and the disease responds to immunosup-
Histologically, the skin lesions are characterized by a pressive therapy, immune‐dysregulatory mechanisms
nodular to diffuse infiltrate that extends from middermis are likely involved.
to the subcutaneous tissue. The infiltrate is perivascular
and periadnexal. Early lesions have a linear or nodular Signalment
configuration, but it may become diffuse in chronic cases. Systemic histiocytosis was first recognized in Bernese
The infiltrate can invade the wall of blood vessels, causing mountain dogs, but since then has been described in sev-
focal or multifocal areas of ischemic necrosis. Important eral other breeds. In one report including 26 dogs,
differential diagnoses for histopathology include sterile Bernese mountain dogs were overrepresented (11/26),