Acetylcholine receptor antibody panel (ACHR Ab, Anti-ACHR antibody

🎯IMMUNOLOGY FLASHCARDS🎯

Acetylcholine receptor antibody panel
(ACHR Ab, Anti-ACHR antibody)

🔹Type of test Blood Normal findings ACh receptor (muscle) binding antibodies:

✏< 0.02 nmol/L ACh receptor (muscle) modulating antibodies

✏0%-20% (reported as % loss of ACAR) Striational (striated muscle) antibodies

✏< 1:60 Test explanation and related physiology .

🔹These antibodies may cause blocks in neuromuscular transmission by interfering with the binding ofacetylcholine (ACh) to AC receptor (ACR) sites on the muscle membrane, thereby preventing muscle contraction.

🔹 This phenomenon characterizes myasthenia gravis (MG).

🔹 Antibodies to ACER occur in more than 85% of patients with acquired MG.
🔹Lower levels are seen in patients with ocular MG only.

🔹 The presence of these antibodies is virtually diagnostic of MG, but a negative test result does not exclude the disease.

🔹 The measured titers do not correspond well with the severity of MG in different patients.

🔹In an individual patient, however, antibody levels are particularly useful in monitoring response to therapy.

🔹As the patient improves, antibody titers decrease. In adults with MG, there is at least a 20% occurrence of thymoma or other neoplasm.

🔹Neoplasms are an endogenous source of the antigens driving production of ACHR autoantibodies.

🔹The ACHR-binding antibody can activate complement and lead to loss of ACER.

1) The AChR-modulating antibody causes receptor endocytosis, resulting in loss of ACAR expression, which correlates most closely with clinical severity of disease.

🎯It is the most sensitive test. A positive modulating antibody test result may indicate subclinical MG, contraindicating the use of curare-like drugs during surgery.

2) The AChR-blocking antibody may impair binding of Ach to the receptor, leading to poor muscle contraction.

🎯It is the least sensitive test (positive in only 61% of patients with MG)

3) Antistriated muscle antibody (striated muscle antibody, LOG) titers greater than or equal to 1:80 are suggestive of myasthenia.

🎯This antibody is detectable in 30% to 40% of anti-AChR-negative patients (particularly those with bulbar symptoms only). However, striated muscle antibody can be found in rheumatic fever, myocardial infarction, and a variety of postcardiotomy states.

🎯✏ Interfering factors 🎯✏

🔎📌 False-positive results may occur in patients with:_

1. amyotrophic lateral sclerosis who have been treated with cobra venom.
2. penicillamineinduced or Lambert-Eaton myasthenic syndrome.
3. autoimmune liver disease
4. Drugs that may cause increased levels include muscle paralytic medicines (succinylcholine) and snake venom.

5- Immunosuppressive drugs may suppress the formation of
these antibodies in patients with subclinical MG.

🎯 Abnormal findings 🎯

A Increased titer levels:

1- Myasthenia gravis
2- Ocular myasthenia gravis
3- Thymoma