Introduction to the Peripheral Nervous System Flashcards
Features of Radiculopathy
Dermatome: Skin area supplied by a single spinal root.
Myotome: Muscle group supplied by a single spinal root.
Sclerotome: Area of bone supplied by a single spinal root.
Most common levels involved:
– Cervical C5-6 = C6 nerve root compression C6-7 = C7 nerve root compression
– Lumbar L4-L5 = L5 nerve root compression
L5-S1 = S1 nerve root compression
Root, Pain, Sensory, Weakness, DTR Loss
Cervical Radiculopathy
C5- pain in scapula and shoulder. sensed in the lateral arm, demostrating shoulder abduction weakness. there is DTR loss of biceps
C6- pain in the scapula, shoulder, proximal arm. sensation in 1st, 2nd, digit and lateral arm, weakness in shoulder abduction and elbow flexion. DTR loss in biceps
C7-pain in scapula, shoudler/arm, and elbow/. sensation in 3rd digit, weakness in elbow extension, wrist, extension, finger extension, DTR loss in triceps
C8- pain in Scapula, shoulder/arm, medial forearm, sensation in 4th and 5 digits, weakness in finger abduction and flexion. Loss of DTR in finger flexors
Lumbosacral Radiculopathy
L4- pain in anteriolateral thigh, knee, medial calf, sensaton in medial calf, weakness, in hip flexion and knee extension, DTR loss in patella
L5- pain in dorsal thigh, and lateral calf, sensation in lateral calf and dorsum foot. weakness in hamstrings, foot dorsiflexion, inversion, eversion, no loss in DTR
S1: pain in posteior thigh, posterior calf, sensation in posteriolateral calf, and lateral foot, weakness in hamstring anf foot plantar flexion, loss of DTR in achilles
Dermatome Map
Hallmarks to Note:
- C6 – Thumb/Index Finger
- C7 – Middle Finger
- C8 – Fourth/Fifth Finger
- T1 – Medial forearm
- T4 – Nipple line
- T10 – Umbilicus
- L1 – Inguinal
- L4 – Medial calf
- L5 – Lateral calf
Brachial Plexopathy
Etiology
Compression/stretch (CABG)
Inflammatory/Idiopathic (Parsonage-Turner)
Radiation Injury (Upper trunk, lateral cord, painless)
Neoplastic (medial cord, painful [Breast, lung])
Traumatic Injury (Traction, laceration, missile)
Ischemia (Diabetic, usually lumbar)
PERIPHERAL NEUROPATHY
• Mononeuropathy
– single nerve is affected
– specific pattern of sensory loss
– weakness only in specific muscle(s)
Polyneuropathy
– diffuse, symmetrical disease
– motor, sensory, or both
– stocking/glove sensory loss
– distal weakness, possibly atrophy
– hypo or arreflexia
• Mononeuropathy Multiplex
- focal involvement of two or more nerves
- may occur in some systemic disorders (DM, vasculitis)
Symptoms of Peripheral Nerve Disease
Sensory
Negative-Loss of sensation
Positive-Paresthesias - Secondary to large myelinated fiber disease (pin and needles)
Pain– Secondary to small unmyelinated fiber disease
- Burning sensations
- Dysesthesia – pain upon gentle touch
- Hyperalgesia – lowered threshold to pain
- Hyperpathia – pain threshold is elevated, but pain is excessively felt.
Motor
- Distal weakness
- Cramps
- Muscle fasciculations (twitching)
- Atrophy • Decreased deep tendon reflexes
- Reduced tone
Motor
- Atrophy (wasting of muscle mass)
- Muscular weakness
- Depressed or absent deep tendon (muscle stretch) reflexes
- Fasciculations
- Cramps
Central patterns: upper motor neuron: spastic, hyperactive DTR, Babinski sign positive
PNS: lower motor neuron-distal, flaccid, atrophic muscles wiht some fasciculations, hypoactive DTR, and loss of sensory in the hands and feet
Median Mononeuropathy Pronator Syndrome
Insidious onset of diffuse/dull ache about the proximal forearm (rarely acute sharp pain).
Pain exacerbation with forced forearm pronation.
Easy fatigue of the forearm muscles.
Diffuse numbness of the hand mostly involving the 2nd - 3rd fingers.
Absence of nocturnal awakening because of pain or numbness.
Median Mononeuropathy: Anterior Interosseous Syndrome
Nerve Conduction Studies: Routine median and ulnar studies are normal
Ulnar Mononeuropathy Common Sites
- Axilla
- Elbow – between medial epicondyle and olecranon
- Cubital tunnel – between tendinous arch of FCU (overrated)
- Wrist – Guyon’s canal
EMG may show abnormalities in:
1st dorsal interosseous
Abductor digiti minimi
Adductor policis
Flexor carpi ulnaris
Flexor digitorum profundus
remember Froment Sign
Radial Mononeuropathy Common Sites
- Axilla – Crutch Palsy
- Humerus/Spiral Groove – “Saturday Night Palsy” – most common
- Supinator (Posterior Interosseus Branch)
- Wrist (Superficial Radial Sensory Branch)
As the radial nerve winds around the humerus, it is vulnerable to compression (Saturday night palsy)
Radial nerve damage leads to the readily recognizable wrist drop that results from paresis of the extensor muscles of the wrist, finger and thumb.
Radial Mononeuropathy
Spiral Groove – “Saturday Night Palsy”
Clinical Features
- Compressive lesion with good prognosis
- Weakness of wrist & finger extension
- Elbow extension (triceps) spared
- Brachioradialis +/- spared
- +/- sensory loss dorsal thumb web
EDX Features
- Radial motor and sensory studies often normal
- EMG findings in extensors of wrist and digits and perhaps brachioradialis
Peripheral Neuropathy
Usually symmetric
- May be motor, sensory, autonomic or combination
- Usually progressive, but not always
- Acquired or inherited
Motor: weakness, atrophy, hypo or arreflexia, cramps, fasciculations
Sensory: “Large fiber” – position/vibratory sense “Small fiber” – pain/temperature sense
Pain, sensory loss, weakness occurs symmetrically and most severely in the distal portions of the limbs.
- The legs are usually affected first and more severely than the arms.
- This distribution is termed “stocking-glove”.
Small Fiber Polyneuropathy
Symptoms –
Pain
– “Burning” dysesthesias
-• Due to spontaneous activity in damaged small-fibers
– Paresthesias
– Temperature sensation abnormalities
Signs
– Decreased pin-prick and temperature sensation
– Dysesthesias to light touch
– Normal strength, reflexes, proprioception, vibratory sensation
EMG/NCV normal
Decreased epidermal nerve fiber density (on skin biopsy)
Diabetes Mellitus
Most common identifiable cause of neuropathy in the United States
• Forms
– Distal sensorimotor neuropathy
– Cranial neuropathy (CN III, CN VI, CN VII)
– Mononeuropathy (carpal tunnel, etc.)
– Mononeuropathy multiplex
– Autonomic neuropathy
– Lumbosacral plexopathy (diabetic amyotrophy)
– Radiculopathy
Charcot-Marie-Tooth Neuropathies
HMSN I (CMT I)
Autosomal dominant
Most common – Demyelinating
Onset 1st or 2nd decade
Often see difficulty walking or running first
Distal symmetric atrophy (legs>arms)
Arreflexia
Mild sensory loss
Skeletal deformities (pes cavus, hammer toes, scoliosis)
EMG shows slowing of motor nerve conduction velocities (i.e. demyelination)
HMSN II (CMT II)
Autosomal dominant
Onset in adulthood
Distal symmetric atrophy (legs>arms)
Arreflexia Mild sensory loss
EMG shows normal or nearly normal motor nerve conduction velocities (i.e. axonal loss)
HMSN III (CMT III or Dejerine-Sotas)
Very severe demyelinating neuropathy of childhood
OTHER HEREDITARY POLYNEUROPATHIES
Porphyria – defect in heme biosynthesis Hereditary neuropathy with liability to pressure palsies
Fabry’s Disease – α galactosidase deficiency
Metachromatic Leukodystrophy – arylsulfatase A deficiency
Globoid Cell Leukodystrophy
Phytanic Acid Storage (Refsum’s) Disease
Tangier Disease – deficiency in HDL
Abetalipoproteinemia (Bassen-Kornzweig’s Syndrome)
Familial Amyloid Neuropathies
ACQUIRED POLYNEUROPATHIES
Acute inflammatory demyelinating polyneuropathy (AIDP, Guillain – Barre Syndrome)
- Chronic inflammatory demyelinating polyneuropathy (CIDP)
- Multifocal motor neuropathy (MMN)
- Multifocal acquired demyelinating sensory and motor neuropathy (MADSAM)
Guillain-Barre Syndrome
Acute/subacute ascending motor paralysis
• Often an antecedent illness, surgery, immunization
– Viral syndrome
- Epstein-Barr
- Mycoplasma pneumonia
- Campylobacter jejuni enteritis
- HIV
- Hodgkin’s disease
Guillain-Barre Syndrome
Low back/leg pain possible at onset
Ascending usually symmetric weakness
Hypo or absent deep tendon reflexes
No/minimal sensory symptoms or signs
Possible respiratory failure, autonomic involvement
Key Laboratory Findings
CSF: albumino-cytologic dissociation ( increasedprotein/ normal cell count/normal glucose)
NCVs: slow conduction velocity, focal conduction block, prolonged F- waves
Treatment
General supportive care with attention to
Swallowing
Respiration
Cardiovascular
Infection
Deep vein thrombosis
Direct treatment with plasma exchange or IVIg
Miller-Fisher Syndrome
– 5% of GBS Cases
- ophthalmoplegia, ataxia, arreflexia
- facial weakness, dysarthria, dysphagia also possible
- GQ1b and GT1a antibodies
Acute Motor Axonal Neuropathy (AMAN)
- GM1, GM1b, GD1a antibodies
Acute Motor and Sensory Neuropathy (AMSAN)
- GM1, GM1b, GM1a antibodies
Chronic Inflammatory Demyelinating Polyneuropathy (CIDP)
Similar to GBS (AIDP) but slower to evolve and more persistent (i.e. ≥ 2 mos.)
- May occur de novo or as sequellae of GBS
- Progressive or relapsing course
- 15% have a monoclonal antibody (IgM or IgG)
- Treatment: IVIg, steroids, plasma exchange, immunosuppressive agents
Multifocal Motor Neuropathy
Clinical
- Adults, male>female, initially in distribution of a single nerve
- Slowly progressive distal weakness of hands>feet
- No sensory signs/symptoms, no UMN signs
• Lab
- Elevated serum GM-1 antibody in 50 – 80%
- EMG shows conduction block or other demyelinating features
- CSF usually normal
• Treatment
- IVIg is treatment of choice - Other immunosuppressants as secondary option
