Peripheral Neuropathy
John Fothergill (1712 – 1780)
First, to describe neuropathic pain
2) Approach
- System
- Distribution
- Onsent
- Comorbidities & medications
- Basic labs & EMG
3) What system is involved (motor, sensory, autonomic, or mixed)?
a. Sensory involvement
- Positive neuropathic sensory symptoms – suggest acquired polyneuropathy
> prickling, tingling, asleep-like numbness
- Pain – suggests Small fiber neuropathy due to toxic, metabolic, ischemic, or idiopathic cause
> electric shock, burning, freezing, tightness, throbbing, allodynia (discomfort or pain to apparently painless stimuli), hyperalgesia (exaggerated pain response)
> often accompanied by reduced or absent sensation of pinprick or temperature
- Negative neuropathic sensory symptoms – suggest acquired or inherited cause
> loss of sensation, imbalance
b. Motor involvement
- Often combined with sensory symptoms:
- Motor > Sensory: Immune-mediated like GBS & CIDP
- Sensory > Motor: In many other polyneuropathies, especially length-dependent neuropathies caused by metabolic or toxic disorders
c. Autonomic involvement
- Symptoms include lightheadedness, syncope, diarrhea, constipation, postprandial bloating, early satiety, urinary complaints, erectile dysfunction, abnormal or absent sweating, and dry mouth and eyes.
4) Where (distribution of nerve involvement)?
a. Distal (length-dependent) and symmetric: metabolic, toxic, inherited, or idiopathic
b. Not length-dependent and asymmetric: immune-mediated or infectious
5) When (onset and course)?
Acute (<1 month) and subacute (1-2 months): immune-mediated or Infectious process
Chronic (>2 months): inherited, metabolic, toxic, or idiopathic
6) What setting – review of comorbidities and medications?
Common causes of acquired polyneuropathies.
Positive family history of high arched foot or hammer toes – Charcot Marie Tooth (CMT) Disease i.e., Hereditary Sensory and Motor Neuropathy
7) Electrodiagnostic test
Define – distribution and extent of neuropathy
Differentiate – axonal and demyelinating or mixed process
Limitation – normal in small fibre neuropathy (skin biopsy is helpful in these cases)
8) Blood tests
a. For distal symmetric neuropathy:
CBC, BMP (Cr, Ca), A1c, TSH, HIV, HCV, B12, folate, and SPEP
b. Specific:
Metabolic/toxic:
Elevated MCV: alcoholism, vitamin B12 deficiency
Thiamine deficiency: alcoholism, bariatric surgery
Urine heavy metals: Heavy metal intoxication
Thyroid function tests: Hypothyroid neuropathy (rare)
Inflammatory:
CBC: mononeuritis complex
Markers or vasculitis or systemic inflammation (ESR, ANCA, RF, ANA, cryoglobulins): Vasculitis, Cryoglobulinemic neuropathy (Hepatitis C)
CSF: protein elevation in AIDP and CIDP
Neoplastic/Paraneoplastic:
Paraneoplastic serology: especially subacute and severe neuropathy in smokers
Chest X-ray and other imaging for cancers: Small cell lung cancer and other malignancies
CSF cytology: carcinomatous or lymphomatous polyradiculopathy
Infections:
CSF: pleocytosis
Lyme titres (serum, CSF): Lyme neuroborreliosis
HIV testing: HIV-associated neuropathy
Hepatitis C (Cryoglobulin testing): Hepatitis C – mixed cryoglobulinemia