HP? Dell? – What is the differential of IBM?

This last week we spent a lot of time on straightforward topics that already have been covered in this blog, so that I did not add any entries. Yesterday, we discussed the case of an inpatient admission for workup of presumed myopathy, aiming at the differential of dermatomyositis/polymyositis vs. motor neuron disease vs. inclusion body myositis. We reviewed the core clinical characteristics – which used to be quite helpful in differentiating them. The problem is that with increasing knowledge and changing diagnostic criteria, the margin is blurred, in particular between the real inflammatory myositides and IBM, where some cases of PM turn out to be IBM in the second biopsy. Also “benign CKemia” might be due to IBM.

So here are some core messages:

  • Think of IBM if progress is slow, muscles are affected predominantly asymmetrically and distally. Quadriceps should be in the picture. Pain not.
  • Differentiate MND from IBM by the myotomal pattern, which IBM does not have.
  • Differentiale DM from IBM by skin, pain and pattern.
  • Differentiate PM from IBM by labs and pattern.

What about treatment? Well, IBM has undergone a mutation from a more inflammatory disease (in the old days) to a myodegenerative disease in the 90ies and 00ies to, again, an inflammatory disease again, now that antibodies have been discovered (see in the references). Still, immunosuppressive therapy does not really help, despite the fact, that some fanatics pour tons of IVIGs into these patients. If you try it, you should go steady.

References.

  • The latest review in Sem Neurol 2012  – which I find not to be the best, but it is quite current.
  • These two articles (one, two) in the Annals from a few weeks ago, discussing the intriguing finding of new antibodies against muscle antigens.

Neuromyotonia

We cover a case of Neuromytonia today, starting with symptoms of muscle cramps. This serves to illustrate the differential – an everyday task. Then we discuss Isaacs’ syndrome and consorts (Morvan, limbic encephalitis) and the relation to VGKC-antibodies (a review from the Nervenarzt helps). If we still have time, we dwell on the new discoveries of the proper antigens targeted by those, using this article in Brain 2010.

Autoimmune myopathies

Using a case of Statin-triggered necrotizing myositis we approach the classical autoimmune myopathies from the point of view of an ambulatory care workup.

References:

  • Mammen. Autoimmune myopathies: autoantibodies, phenotypes and pathogenesis. Nature reviews nephrology 2011 – available via Medscape’s Neurology CME section
  • The autoimmune myopathies chapter of the Handbook of Neurology Vol 86
  • The chapter “Idiopathic inflammatory myopathies” of Pourmand’s book on Immune-mediated neuromuscular disorders