Inflammatory myopathy

Thanks Eliot for presenting a great case. This is a case of an elderly gentleman with a history of fibromyalgia, exogenous iodine intake presenting with subacute progressive lower extremity weakness found to have abnormal TFTs and troponemia found to have a biopsy proven idiopathic inflammatory myopathy.

 A) H&E of PM. B) H&E of IBM. From NEJM article below.

A) H&E of PM. B) H&E of IBM. From NEJM article below.

Main Points:

  • 1) The approach to weakness can be thought of as CNS, PNS, oxygen delivery and psych. See this blog post for more information.
  • 2) Patients with a new diagnosis of dermatomyositis and polymyositis should have had age appropriate cancer screening.
  • 3) Iodine is found in many foods including seaweed, kelp, certain medications (eg amiodarone) and in contrast agent. A person with a normal thyroid should be able to regulate excess exogenous iodine intake but someone with hypothyroidism may develop clinical hyperthyroidism.

Want to learn more?

Inflammatory myopathies

  • There are 4 main types of inflammatory myopathies, DM, PM, IBM and necrotizing autoimmune myositis.
  • Key features pre-biopsy/ testing of each include:
    • DM – characteristic skin rash
    • PM – usually diagnosis of exclusion
    • IBM – distal muscle weakness with atrophy of hand muscles
    • NAM – very high CK levels
  • Treatment of dermatomyositis and polymyositis generally consists of steroids. Refractory disease may benefit from rituximab and IVIG.

Here is a great chart from an NEJM review article on inflammatory muscle disorders.

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Abnormal TFTs

  • the differential for a high TSH and normal fT4/T3 includes subclinical hypothyroidism, drugs and euthyroid sick syndrome
  • check T3 if someone has clinical hyperthyroidism but normal TSH/T4

Here is an excellent video by Palo Alto VA Internist/ clinician educator Eric Strong on interpretation of abnormal thyroid function tests.