Sensory Polyneuropathies: Difference between revisions

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The terms "polyneuropathy," "peripheral neuropathy," and "neuropathy" are often often used interchangeably but in fact have distinct definitions.

Peripheral neuropathy refers to any disorder of the peripheral nervous system which can include radiculopathies and mononeuropathies.
Neuropathy is even more general, referring to any disorder of the central and peripheral nervous system
Mononeuropathy means dysfunction of an individual peripheral nerve
Polyneuropathy is a generalised relatively homogenous disease process where many peripheral nerves are affected with the distal nerves being most prominently affected

Anatomy

Characteristics of peripheral nerve fibres

Nerve Fibre	Myelin	Diameter (µm)	Conduction velocity (m/s)	General Function
Aα (I)	Yes	13-20	80-120	Proprioception: muscle spindle primary endings (Ia), golgi tendon organs (Ib), and alpha motor neurons
Aβ (II)	Yes	6-12	35-75	Discriminative sensitivity to mechanical stimuli (touch, vibration), proprioception, pain modulation (block nociceptive information, allodynia in sensitisation)
Aγ	Yes	4-8	15-40	Touch, pressure, and gamma motor neurons.
Aδ (III)	Thin	1-5	5-30	"rapid" pain, crude touch, pressure, temperature. AMH type I for rapid mechanical pain (high heat threshold >53C), AMH type II for rapid heat pain (lower heat threshold 43-47C).
B	No	1-3	3-14	preganglionic autonomic
C (IV)	No	0.2-1.5	0.5-2.0	"second" pain, mechanical, chemical, thermal, pruritis, and postganglionic autonomic. polymodal

Diagnostic Schema

Peripheral neuropathy has many causes. It is not always possible to find the underlying cause. If diagnosis is possible then this enables more accurate prognostication, and potentially treatment for some causes. The differential diagnosis can be categorised in several ways.

Pattern of neurological signs and symptoms: sensory, motor, autonomic or mixed
Distribution of affected nerve: symmetrical versus asymmetrical, and distal versus proximal.
Fibre type involved: Large fibre versus small fibre. Large fibre neuropathies will typically show reduced reflexes, weakness, and reduced vibration and position sense. On the other hand, small fibre neuropathies have normal reflexes and strength, and more minimal findings of reduced sensation to pin prick and temperature.
Pathological process involved: Axonal versus demyelinating. Axonal loss for example in diabetic polyneuropathy, or demyelination for example in CIDP. Polyneuropathies can be associated with axonal loss (e.g., diabetic polyneuropathy) or demyelination (e.g., CIDP)
Time course: acute, subacute, or chronic. An acute onset suggests inflammatory, immunologic, toxic, or vascular aetiologies. Evolution over many years is suggestive of a hereditary or metabolic process.
Hereditary vs acquired: Hereditary polyneuropathies can manifest in adulthood or childhood and there is often a family history. Charcot-Marie-Tooth can be suspected with the presence of a distinctive pes cavus foot.
Primary vs secondary: Primary polyneuropathy e.g. chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), and secondary polyneuropathy e.g. diabetes, toxin, and monoclonal gammopathy.

An example is Guillain Barre-syndrome. This condition manifests with multiple nerve root involvement acutely, and in most cases there is preferential involvement of the myelin sheath. It is therefore described as an acute demyelinating inflammatory polyradiculopathy. Using this schema narrows down the diagnostic possibilities.

Clinical Features

Polyneuropathies

n most polyneuropathies there is impairment of both small and large fibre sensory function i.e. pain and temperature for small-fibre involvement; and joint position and vibration for large-fibre involvement. However some patients may have selective damage to either the small or large fibres.

In those with predominant small fibre neuropathy, they may have burning, painful dysaesthesiae, altered pinprick and temperature sensation, and autonomic dysfunction; but with normal motor function and tendon reflexes.

In those with predominant large fibre neuropathy, there is loss of joint position and vibration sense, ataxia, areflexia, and variable loss of motor function.

Motor Function

In most polyneuropathies motor and sensory symptoms and signs are symmetrical but show a predominantly distal pattern. Usually the lower limbs are affected earlier and more severely than the upper limbs, and the trunk and head are the last to be affected and only in severe cases.

An exception to the standard distal pattern is in acute inflammatory neuropathies. In these situations there can be early involvement of cranial nerves, upper limbs, and the respiratory tract.

Cranial nerve involvement can occur with sarcoidosis, Lyme disease, Sjogren syndrome, metastatic meningeal disease, malignant nerve root infiltration, and rare metabolic neuropathies (Refsum, Tangier, and Riley-Day).

Predominant upper limb symptoms can be seen in Sjogren syndrome, chronic immune neuropathies, prophyria, lead toxicity, amyloid, and some inherited neuropathies.

Tendon Reflexes

Deep tendon reflexes are generally diminished early on in the disease process, and may later become absent. Reflexes may be normal in small fibre neuropathies.

Sensory Function

There is sensory loss in a symmetrical and distal pattern like with motor loss. The sensory loss spreads proximally with worsening of the disease. I

Investigations

Painful neuropathies and their laboratory tests
Neuropathy	Blood	Urine	Biopsy
Diabetic	HbA1c	Glucose
Alcohol	LFTs
Vitamin Deficiency	B12
Vasculitis	Antinuclear antibodies		Biopsy
Sjogrens disease	Sjogren antibodies
AIDS	HIV antibodies, CD4
Primary amyloid	Protein electrophoresis	Protein electrophoresis	Biopsy
Fabry's disease	d-galactosidase Globotriasosylceramide	Globotriasosylceramide
Uraemic	UECs
Porphyric		d-aminolevulinic acid Porphobilinogen
Tangier's disease	Low cholesterol Low HDLs Low apoprotein
Churg-Strauss	Eosinophilia
Heavy metal	Arsenic, thallium
Familial amyloid			Biopsy
Hereditary			Biopsy
Charcot-Marie-Tooth			Biopsy
Cryoglubulinaemic			Biopsy

Reading

Media:Peripheral_Neuropathy_-_Watson_2015.pdf

@@ Line 1: / Line 1: @@
-{{stub}}
+{{stub}}The terms "polyneuropathy," "peripheral neuropathy," and "neuropathy" are often often used interchangeably but in fact have distinct definitions.
-== Taxonomy ==
-The terms "polyneuropathy," "peripheral neuropathy," and "neuropathy" are often often used interchangeably but in fact have distinct definitions.
+* Peripheral neuropathy refers to any disorder of the peripheral nervous system which can include radiculopathies and mononeuropathies.
+* Neuropathy is even more general, referring to any disorder of the central and peripheral nervous system
+* Mononeuropathy means dysfunction of an individual peripheral nerve
 * Polyneuropathy is a generalised relatively homogenous disease process where many peripheral nerves are affected with the distal nerves being most prominently affected
-* Peripheral neuropathy refers to any disorder of the peripheral nervous system which can include radiculopathies and mononeuropathies.
-* Neuropathy is even more general, referring to disorders of the central and peripheral nervous system
 == Anatomy ==
 {{Peripheral Nerve Fibres}}
-== Differential Diagnosis ==
+== Diagnostic Schema ==
-The differential diagnosis for polyneuropathy can be categorised in several ways
+Peripheral neuropathy has many causes. It is not always possible to find the underlying cause. If diagnosis is possible then this enables more accurate prognostication, and potentially treatment for some causes. The differential diagnosis can be categorised in several ways.
+# '''Pattern''' of neurological signs and symptoms: sensory, motor, autonomic or mixed
+# '''Distribution''' of affected nerve: symmetrical versus asymmetrical, and distal versus proximal.
+# '''Fibre type''' involved: Large fibre versus small fibre. Large fibre neuropathies will typically show reduced reflexes, weakness, and reduced vibration and position sense. On the other hand, [[Small Fibre Neuropathy|small fibre neuropathies]] have normal reflexes and strength, and more minimal findings of reduced sensation to pin prick and temperature.
+# '''Pathological process''' involved: Axonal versus demyelinating. Axonal loss for example in diabetic polyneuropathy, or demyelination for example in [[Chronic Inflammatory Demyelinating Polyneuropathy|CIDP]]. Polyneuropathies can be associated with axonal loss (e.g., diabetic polyneuropathy) or demyelination (e.g., [[Chronic Inflammatory Demyelinating Polyneuropathy|CIDP]])
+# '''Time course''': acute, subacute, or chronic. An acute onset suggests inflammatory, immunologic, toxic, or vascular aetiologies. Evolution over many years is suggestive of a hereditary or metabolic process.
+# '''Hereditary vs acquired''': Hereditary polyneuropathies can manifest in adulthood or childhood and there is often a family history. Charcot-Marie-Tooth can be suspected with the presence of a distinctive pes cavus foot.
+# '''Primary vs secondary''': Primary polyneuropathy e.g. [[Chronic Inflammatory Demyelinating Polyneuropathy|chronic inflammatory demyelinating polyradiculoneuropathy (CIDP)]], and secondary polyneuropathy e.g. diabetes, toxin, and monoclonal gammopathy.
+An example is Guillain Barre-syndrome. This condition manifests with multiple nerve root involvement acutely, and in most cases there is preferential involvement of the myelin sheath. It is therefore described as an acute demyelinating inflammatory polyradiculopathy. Using this schema narrows down the diagnostic possibilities.
+== Clinical Features ==
+=== Polyneuropathies ===
+n most polyneuropathies there is impairment of both small and large fibre sensory function i.e. pain and temperature for small-fibre involvement; and joint position and vibration for large-fibre involvement. However some patients may have selective damage to either the small or large fibres.
+In those with predominant small fibre neuropathy, they may have burning, painful dysaesthesiae, altered pinprick and temperature sensation, and autonomic dysfunction; but with normal motor function and tendon reflexes.
+In those with predominant large fibre neuropathy, there is loss of joint position and vibration sense, ataxia, areflexia, and variable loss of motor function.
+'''Motor Function'''
+In most polyneuropathies motor and sensory symptoms and signs are symmetrical but show a predominantly distal pattern. Usually the lower limbs are affected earlier and more severely than the upper limbs, and the trunk and head are the last to be affected and only in severe cases.
+An exception to the standard distal pattern is in acute inflammatory neuropathies. In these situations there can be early involvement of cranial nerves, upper limbs, and the respiratory tract.
+Cranial nerve involvement can occur with sarcoidosis, Lyme disease, Sjogren syndrome, metastatic meningeal disease, malignant nerve root infiltration, and rare metabolic neuropathies (Refsum, Tangier, and Riley-Day).
+Predominant upper limb symptoms can be seen in Sjogren syndrome, chronic immune neuropathies, prophyria, lead toxicity, amyloid, and some inherited neuropathies.
-. Large fibre vs small fibre: Large fibre neuropathies will typically show reduced reflexes, weakness, and reduced vibration and position sense. On the other hand, [[Small Fibre Neuropathy|small fibre neuropathies]] have normal reflexes and strength, and more minimal findings of reduced sensation to pin prick and temperature.
+'''Tendon Reflexes'''
-. Hereditary vs acquired: Hereditary polyneuropathies can manifest in adulthood or childhood and there is often a family history. Charcot-Marie-Tooth can be suspected with the presence of a distinctive pes cavus foot.
+Deep tendon reflexes are generally diminished early on in the disease process, and may later become absent. Reflexes may be normal in [[Small Fibre Neuropathy|small fibre neuropathies]].
-. Primary vs secondary: Primary polyneuropathy e.g. [[Chronic Inflammatory Demyelinating Polyneuropathy|chronic inflammatory demyelinating polyradiculoneuropathy (CIDP)]], and secondary polyneuropathy e.g. diabetes, toxin, and monoclonal gammopathy.
+'''Sensory Function'''
-. Axonal vs demyelinating: Axonal loss for example in diabetic polyneuropathy, or demyelination for example in [[Chronic Inflammatory Demyelinating Polyneuropathy|CIDP]]. Polyneuropathies can be associated with axonal loss (e.g., diabetic polyneuropathy) or demyelination (e.g., [[Chronic Inflammatory Demyelinating Polyneuropathy|CIDP]])
+There is sensory loss in a symmetrical and distal pattern like with motor loss. The sensory loss spreads proximally with worsening of the disease. I
 == Investigations ==