View source for WBR0405

 {{WBRQuestion
|QuestionAuthor= {{SSK}} (Reviewed by Serge Korjian)
|ExamType=USMLE Step 1
|MainCategory=Pathology
|SubCategory=Renal
|MainCategory=Pathology
|SubCategory=Renal
|MainCategory=Pathology
|SubCategory=Renal
|MainCategory=Pathology
|MainCategory=Pathology
|MainCategory=Pathology
|SubCategory=Renal
|MainCategory=Pathology
|SubCategory=Renal
|MainCategory=Pathology
|SubCategory=Renal
|MainCategory=Pathology
|SubCategory=Renal
|MainCategory=Pathology
|MainCategory=Pathology
|SubCategory=Renal
|Prompt=A 67-year-old African-American woman with history of end-stage renal disease on hemodialysis presents to the physician with right wrist pain.  The patient explains that she has tingling and burning sensation in the right hand along the thumb, index, and middle part of the fourth finger. The symptoms also seem to worsen at night, making it difficult for her to fall asleep.  On physical examination, the patient has asymmetric weakness of thumb adduction with thenar atrophy. Tinel's sign and Phalen's maneuver are both positive.  Accumulation of which product is most likely to be present in this patient’s condition?
|Explanation=[[Carpal tunnel syndrome]] (CTS) is an entrapment neuropathy of the median nerve that causes pain, paresthesias, and burning sensation along the distribution of the distal median nerve. CTS occurs more commonly in females than in males. Symptoms usually worsen throughout the day and are most prominent at night. It is commonly bilateral, but patients frequently have clinical manifestations unilaterally. In [[hemodialysis]] patients, CTS is due to β2-microglobulin associated amyloidosis .  Tinel and Phalen signs are both helpful in the diagnosis of carpal tunnel syndrome. However, they are not very specific or sensitive. The diagnosis is mostly clinical, but electromyography (EMG) and nerve conduction studies are sometimes helpful.

Other common entrapment neuropathies include ulnar tunnel, where the ulnar nerve is commonly compressed at Guyon’s canal as it enters the wrist along with the ulnar artery.  Tarsal tunnel syndrome (posterior tibial neuralgia) is a compression of the posterior tibial nerve as it passes in the anatomical tarsal tunnel, posterior to the medial malleolus.
|AnswerA=Amyloid light-chain (AL)
|AnswerAExp=Amyloid light-chain (AL) amyloidosis is due to deposition of Ig light chains.  It is commonly associated with multiple myeloma.
|AnswerB=β2-microglobulin
|AnswerBExp=β2-microglobulin deposition in patients on hemodialysis causes symptoms of entrapment neuropathy, such as carpal tunnel syndrome.
|AnswerC=Amylin
|AnswerCExp=Amylin or Islet Amyloid Polypeptide (IAPP) is produced in the beta cells of the pancreas.  Amylin amyloidosis is associated with diabetes mellitus.
|AnswerD=A-Cal
|AnswerDExp=A-Cal protein from calcitonin is seen in patients with medullary thyroid cancer.
|AnswerE=β-Amyloid
|AnswerEExp=β-Amyloid is the main component of amyloid plaques associated with Alzheimer’s disease.
|EducationalObjectives=Carpal tunnel syndrome (CTS) is an entrapment neuropathy of the median nerve.  β2-microglobulin amyloidosis is commonly a cause of CTS in patients on chronic hemodialysis.
|References=Ullian ME, Hammond WS, Alfrey AC, et al.  Beta-2-microglobulin-associated amyloidosis in chronic hemodialysis patients with carpal tunnel syndrome.  Medicine (Baltimore).  1989;68(2):107-15.
|RightAnswer=B
|WBRKeyword=Amyloidosis, Carpal tunnel syndrome, CTS, Hemodialysis, ESRD, End-stage renal failure, Entrapment neuropathies
|Approved=Yes
}}