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.
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History of polyneuropathy

As one of my mentors taught, polyneuropathy is all about history taking. The rest might be physical examination. Finally some lab tests. Before you then dare enter the neurophysiological approach all the data before should be ready, so that you can do a proper electrophysiological workup.

So here is my mental structure for the initial approach of polyneuropathy.

  1. What is the time course of complaints?
  2. Which fiber types are affected and how (positive and negative symptoms)?
  3. What distribution pattern do the symptoms have?
  4. What is the pathophysiology of the symptoms? (axonal vs demyelinative)
  5. What other disease might the patient have?
  6. What drugs and toxins did the patient suffer?
  7. What is the family history?

Here is a list of positive and negative symptoms for the various fiber types (see 2):

Fiber type Negative Positive
Motor Weakness, Hyporeflexia, Hypotonia, Deformities Fasciculations, Crampi, restless legs
Sensory, large fiber Hypesthesia, Hypotonia, Pallhypesthesia, Ataxia Tingling, pins and needles
Sensory, small fiber Hypalgesia, Thermhypesthesia Burning, Jabbing, Shooting
Autonomic Orthostatic hypotension, Arrhythmia, decreased sweating, constipation, impotence, urinary retention, … Labile blood pressure, arrhythmia, increased sweating, diarrhea, urge incontinence, …

There are a few special cases of polyneuropathy with only limited differential:

  1. Acute polyneuropathies: GBS, porphyria, diphtheria, drugs (dapson, nitrofurantoin, vincristine), toxins (arsenic, thallium), Lyme, vasculitis
  2. Predominantly motor polyneuropathy: lead poisoning, porphyria, CMT, CIDP/GBS
  3. Pure sensory polyneuropathy: paraneoplastic, postinfectious, Sjögren, B6 hypervitaminosis, inherited, Friedreich
  4. Predominantly small fiber: diabetes, amyloid, toxic (alcohol), drugs (DDI, DDC), hypertriglyceridemia, hereditary, M. Tangier, M. Fabry, AIDS, idiopathic
  5. Predominantly proximal polyneuropathy: diabetes, prophyria, CIDP
  6. Asymmetric: mononeuritis multiplex, CIDP or PNP + entrapment/radiculopathy
  7. Mononeuritis multiplex: vasculitis, diabetes, CIDP, HNPP, infectious (leprosy, Lyme, HIV), infiltrative (sarcoid, meningeosis)
  8. Painful: small fiber, vasculitis, GBS
  9. Demyelinating acquired: GBS, CIDP (+- HIV, IgM, anti-MAG, myeloma/Waldenström), GM1, diphtheria, toxic (amiodarone, arsenic)