Derm 13 - immune diseases Flashcards
dematologic immune-mediated diseases
- how common?
- easily diagnosed?
- when should we intervene?
Uncommon to Rare
Oftentimes over suspected or missed
Early intervention may lead to faster control
> On the other hand, overdiagnosis of immune mediated disease leading to immunosuppressive treatment of a patient with a poorly responsive parasitic, bacterial or fungal disease could be disastrous!
most common immune skin disease seen in clinical practice
Pemphigus Foliaceus (PF)/ Pemphigus Erythematosus (PE)
Pemphigus Foliaceus (PF)/ Pemphigus Erythematosus (PE) in the dog
- etiology
- relationship between these conditions?
- occurrence
- how cells are affected
- lesion appearance and distribution
- This is a disease that results from a pathological loss of adhesion between keratinocytes secondary to immune attack on the desmosome, the links between the corneocytes of the skin
> In dogs, it is highly suspicious that the target antigen is desmocollin-1, especially in facial predominant cases.
<><> - PE is considered by many these days to be a milder form of PF (It was once considered a crossover disease between PF and DLE)
<><> - Can occur spontaneously or can be associated with tumors or drug administration
<><> - Desmosomal attack results in the formation of rounded keratinocytes, or acantholytic keratinocytes (not acanthocytes)
<><> - In dogs this results in a pustular dermatitis often associated with honey coloured crusts
> can be confused with a pyoderma. However, in general, the lesions appear more generalized and pustular compared with pyoderma cases - Trunk and head (including pinnal) distribution is common; footpads are affected in 35% of cases
- Lesions are restricted to the face in 16-24% of cases and 58% progress to include the trunk.
Pemphigus Foliaceus (PF)/ Pemphigus Erythematosus (PE) in the dog
- Dx?
- what else should we consider?
- presence of acantholytic keratinocytes are highly suggestive of a diagnosis.
> However, the presence of these cells in small numbers is not pathognomonic for PF
> Indeed dermatophytosis (trichophyton spp.) and bacterial infection can also result in acantholytic keratinocytes (AK’s) - The presence of bacteria along with a small number of AK’s on cytology should lead one to begin antibiotic treatment (+/- bacterial culture) before considering pemphigus
- Fungal culture should be routinely performed as well in patients slated for biopsy
Pemphigus Foliaceus (PF)/ Pemphigus Erythematosus (PE) in the dog
- signalment
- Middle age – mean age of onset 4-6 years but can occur at any age
- Breed predisposition:
◦ Akita, Chow Chow overrepresented but also seen commonly in Cocker Spaniel, Dachshunds and Labrador Retrievers but can be any breed
conditions that look like pemphigus
- dematophytosis
- pyoderma
PF treatment vs biopsy - which should we do first and why?
I will treat patients with antibiotics for at least 2 weeks before performing a biopsy. It is not uncommon for patients with PF to have secondary infections and the presence of infection in the biopsy sample will complicate the diagnosis
<><>
- Tx with antibiotics before Bx
> improved success rate? fewer euthanasias?
<><>
The long term benefit of treating PF patients with antibiotics before or when starting treatment is controversial. It was reported to improve outcome, but in a more recent reviews by Mueller, there were no significant differences in success rate with early antibiotic treatment
<><>
- culture a biopsy
- collect multiple samples
PF treatment
- glucocorticoid success?
- azathioprine and prednisolone?
- prednisolone alone?
- not much difference between any of these
PF success rate with exclusive glucocorticoid therapy? prognositc sign?
<50%, with a favorable response within the first 10 days of treatment being a good prognostic sign
PF treatment with immunosuppression success rate?
- 52% went into remission with treatment
- 35% improved greatly but still had focal lesions
- 13% euthanized
PF most common treatment? dosing?
- Most commonly, prednisone or prednisolone is administered at immunosuppressive dosages
- lately the tendency is not to use the top end doses in most cases
- divide the dose into 2 treatments BID
- If a favorable response is seen within 10–14 days this dosage is reduced to SID
- If the response continues to be very good, I will decrease doses by 25% for 28 days and then lower to an alternate day basis with the goal of dosing at 1 mg/kg every 48 h or less
PF treatment for ‘stubborn spot’
I have found 0.1% tacrolimus to be very useful for stubborn spots / localized cases
alternate steroids vs prednisone for PF?
- Too PU/PD? Consider drugs with less mineralocorticoid activity
> methylprednisolone at similar dosage - Dexamethosone more potent, but watch out for side effects (GI bleed)
What can we do if we are treating PF and there is a poor / inadequate response to steroids?
- start azathioprine in the dog (do not use azathioprine in the cat.)
- Chlorambucil for cats
adverse reactions to azathioprine
- Hepatotoxicity
- pancreatitis
- Myelosuppression (lymphopenia, anemia and leukopenia)
- Diarrhea (which can be severe and lead to discontinuation of the drug)
- Increased susceptibility to opportunistic infection when used long term
> pyoderma, demodicosis, dermatophytosis
<><><><>
Thiopurine methyltransferase - metabolizes AZA
> 0.8% of population have low levels and are susceptible to bone marrow dyscrasias
> some have too much and need a higher dose
