Category: Diagnosing DH

1. How is dermatitis herpetiformis diagnosed?
2. How accurate is the skin biopsy?
3. How accurate are the blood tests?
4. Can the taking of dapsone be used as a diagnostic tool?
5. What's an endoscopy and why do DH patients need one?

1. How is dermatitis herpetiformis diagnosed?
   
   The diagnosis of DH is made by a simple skin test. A small piece of skin approximately 3 mms in diameter is taken from an unaffected area, ie. normal looking skin. The skin is examined for the presence of a substance called IgA (immunoglobulin A) and is found at a specific site in the skin. Although the test is simple, it is important a laboratory experienced in the procedure undertakes the examination of the skin.
   
   The diagnosis of DH can also be confirmed with the same tests as used for diagnosing coeliac disease, ie. a small intestinal biopsy and blood tests looking for specific antibodies, called anti-endomysial and tissue transglutaminase antibodies. Occasionally in DH, the blood tests may be negative because their positivity correlates strongly with the severity of the intestinal lesion.
   
   (Source - Medical Article)
   
   
   
   
2. How accurate is the skin biopsy?
   
   The skin biopsy is a specialized test using immunofluorescence. A patient needs to find a doctor and laboratory experienced in the procedure. If the correct immunogloblin is found in the skin then it is almost 100% certain that a patient has DH, whereas if it is not found, the diagnosis is not certain.
   
   (Source - Forum Contributors)
   
   
   
   
3. How accurate are the blood tests?
   
   Blood tests can be a bit hit and miss. There are a couple of types and the newer of the two can give about a 97% accurate positive diagnosis - tTG (tissue transglutaminase IgA autoantibody). The 97% is useful for "true positives" - that is to say when a result is positive for coeliac disease it is 97% certain that the positive result is actually true, 3% chance that it is not true.
   
   The true and false "negative rates" are much worse for the tests. Basically, if they are negative, nothing can be accurately deduced.
   
   It is possible to have negative blood tests and still have villous atrophy, albeit maybe partial villous atrophy. The only way to be certain of a diagnosis of coeliac disease is to perform an intestinal biopsy.
   
   (Source - Forum Contributors)
   
   
   
   
4. Can the taking of dapsone be used as a diagnostic tool?
   
   Dapsone is an old antibiotic that, when taken for a few days, suppresses the DH rash. It needs to be taken with caution as it can lead to some nasty side effects (see DH drugs Q's & A's). Regular blood tests should be obtained whilst taking this drug.
   
   Diagnosis is usually made with several factors taken into consideration, not just dapsone and primary spot symptoms. Blood tests, skin and intestinal biopsies, prior medical history, all build up a picture for narrowing down the statistical possibilities of misdiagnosis. Also the test does not rule out a bacterial infection if the spots improve, but it is a very useful indicator.
   
   (Source - Forum Contributors)
   
   
   
   
5. What's an endoscopy and why do DH patients need one?
   
   An endoscopy, more specifically a gastroscopy, involves a thin, flexible tube being passed through the mouth into the gut in order to obtain a tiny sample of the small bowel lining. The test is usually done under sedation, and the sedative drug often causes people to have no recollection of the test.
   
   Because DH patients also have coeliac disease, it is necessary to take an intestinal biopsy to confirm the diagnosis. In these patients gluten damages the lining of the small intestine which greatly reduces the ability of the gut to absorb adequate nutrients from food. The sample is checked in a laboratory to establish this damage before placing a person on a lifelong diet.
   
   (Source - Forum Contributors)