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.
- What is the time course of complaints?
- Which fiber types are affected and how (positive and negative symptoms)?
- What distribution pattern do the symptoms have?
- What is the pathophysiology of the symptoms? (axonal vs demyelinative)
- What other disease might the patient have?
- What drugs and toxins did the patient suffer?
- What is the family history?
Here is a list of positive and negative symptoms for the various fiber types (see 2):
|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:
- Acute polyneuropathies: GBS, porphyria, diphtheria, drugs (dapson, nitrofurantoin, vincristine), toxins (arsenic, thallium), Lyme, vasculitis
- Predominantly motor polyneuropathy: lead poisoning, porphyria, CMT, CIDP/GBS
- Pure sensory polyneuropathy: paraneoplastic, postinfectious, Sjögren, B6 hypervitaminosis, inherited, Friedreich
- Predominantly small fiber: diabetes, amyloid, toxic (alcohol), drugs (DDI, DDC), hypertriglyceridemia, hereditary, M. Tangier, M. Fabry, AIDS, idiopathic
- Predominantly proximal polyneuropathy: diabetes, prophyria, CIDP
- Asymmetric: mononeuritis multiplex, CIDP or PNP + entrapment/radiculopathy
- Mononeuritis multiplex: vasculitis, diabetes, CIDP, HNPP, infectious (leprosy, Lyme, HIV), infiltrative (sarcoid, meningeosis)
- Painful: small fiber, vasculitis, GBS
- Demyelinating acquired: GBS, CIDP (+- HIV, IgM, anti-MAG, myeloma/Waldenström), GM1, diphtheria, toxic (amiodarone, arsenic)