Approach to bilateral LMN weakness Flashcards
Approach to bilateral LMN weakness without sensory loss
Approach to bilateral LMN weakness with sensory loss
Neuro-localisation of bilateral LMN weakness
LMN weakness with NORMAL sensation
- Anterior horn cell
- Pure motor neuropathy
- Neuromuscular junction
- Muscle myopathy
LMN weakness with ABNORMAL sensation
- Cauda equina syndrome
- Root or plexus lesion
- Peripheral neuropathy (distal > proximal)
- Mononeuritis multiplex
Bilateral proximal LMN quick screening routines
- Limb inspection - shortened, wasted limb (old polio)
- Face - ptosis (MG, myotonic dystrophy), facial diplegia and frontal balding (myotonic dystrophy)
- Fatigability (MG)
- Grip and percussion myotonia
- Where is the weakness?
- Proximal: anterior horn, proximal myopathy
- Distal: anterior horn, pure motor neuropathy, distal myopathy - Complications
- Mobility, fine motor, swallowing
- Respiratory failure (not in PACES, but pls mention)
- Additional myotonic dystrophy clues: cataracts, cardiomyopathy, hypogonadism, goitre, DM
- Peripheral sensory loss - ulcers, amputations
Peripheral neuropathy
A. Does this confirm peripheral neuropathy?
1. Symmetrical, distal > proximal weakness
- Distal wasting, bilateral foot drop, high stepping gait
2. Glove and stocking distal > proximal sensory loss
3. Mixed of predominant sensory, predominant motor, or both
B. Is this inconsistent with peripheral neuropathy?
1. Lower back scar or tuft of hair (low spinal cord lesion)
2. Urine incontinence (autonomic neuropathy vs spinal cord lesion)
3. NOT symmetrical and bilateral, or even localised to myotomes/dermatomes
Poliomyelitis
Level: LMN - hypotonia, areflexia, weakness
Distribution: symmetrical/asymmetrical lower limbs
Sensation: normal
Cerebellar: normal
Additional features: foot drop, limb shortening, wasting, walking aids, childhood or longstanding illness
Myotonic dystrophy
Level: LMN - normal tone, hyporeflexia
Distribution: symmetrical, distal > proximal
Sensation: normal
Cerebellar: normal
Additional features: myotonic facies (frontal balding, ptosis, facial droop, temporal and masseter wasting), ocular eye opening difficulty, grip and percussion myotonia
Myasthenia gravis
Level: LMN - normal tone, hyporeflexia
Distribution: varies, proximal > distal
Sensation: normal
Cerebellar: normal
Additional features: ptosis, fatigability of eyes, limbs, speech
Anterior horn cell diseases (motor neuron disease)
Level: more LMN, can also be UMN
Distribution: proximal > distal or both
Sensation: normal
Cerebellar: normal
Additional features: fasciculation of limbs and tongue, maybe bulbar involvement
What are the proximal myopathies?
- FSHD
- LGMD
- Cushing’s and steroid myopathy
- Thyroid myopathy
- Acromegaly
- Alcohol myopathy
- Duchenne and Becker’s muscular dystrophy
Facio-scapulo-humeral dystrophy (FSHD)
Level: LMN
Distribution: symmetrical, proximal (UL) > distal (foot) (early stage asymmetric)
Sensation: normal
Cerebellar: normal
Additional features: overriding/winged scapula, polyhill sign, facial weakness without ptosis, bilateral foot drop
To consider: oculopharyngeal dystrophy (ocular weakness)
Dermatomyositis
Level: LMN
Distribution: symmetrical, proximal > distal
Sensation: normal
Cerebellar: normal
Additional features: heliotrope rash, photosensitive shawl rash, Gottron’s papules
Endocrine related myopathy
Causes:
1. Cushing’s and steroid myopathy
2. Thyroid (hyper/hypothyroidism(
3. Acromegaly
4. Alcoholic myopathy
Level: LMN
Distribution: symmetrical, proximal (distal involving peripheral neuropathy)
Sensation: normal (abnormal involving peripheral neuropathy)
Cerebellar: normal
Additional features:
- Cushing: central obesity, skin thinning, supraclavicular fat pad, abdominal striae
- Thyroid: goitre, tremor
- Acromegaly: spade-like hands, coarse facies, visual field defect (bitemporal hemianopia)
- Alcoholic: dupuytren’s contracture, parotidomegaly, chronic liver disease
Duchenne or Becker’s muscular dystrophy
Level: LMN
Distribution: symmetrical, proximal > distal
Sensation: normal
Cerebellar: normal
Additional features: calf hypertrophy, Gower sign
Limb girdle muscular dystrophy
Heterogenous group of genetic muscular dystrophy with limb-girdle weakness
Level: LMN, pelvic and shoulder weakness
Distribution: symmetrical, proximal > distal
Sensation: normal
Cerebellar: normal
Additional features: NO facial weakness, maybe winged scapula, cardiomyopathy
Hereditary Sensorimotor Neuropathy (CMT)
Variation of: HSMN (sensorimotor) vs HMN (motor only)
Level: LMN
Distribution: symmetrical, distal weakness
Sensation: normal in HMN, abnormal distal loss in HSMN
Cerebellar: normal
Additional features: inverted champagne bottle (distal wasting), pes cavus, toe clawing, Archilles tendon contracture, thickened nerve
Multifocal motor neuropathy
Level: LMN
Distribution: patchy (symmetric or asymmetrical) distal weakness
Sensation: normal
Cerebellar: normal
Additional features: NCS conduction block
Guillain Barre syndrome
Level: LMN
Distribution: symmetrical, ascending distal to proximal weakness
Sensation: may be normal (AMAN) or abnormal distal to proximal loss (AMSAN)
Cerebellar: normal
Additional features: recent GI symptoms, respiratory failure
Inclusion body myositis
Level: LMN, hyporeflexia due to atrophy
Distribution: asymmetric, distal (hands) to proximal (quadriceps)
Sensation: normal
Cerebellar: normal
Additional features: dysphagia, with sparing of EOM
Cauda equina lesion
Level: myotomal LMN (L4 and below)
Distribution: appears to look distal to proximal but actually not
Sensation: sacral numbness
Cerebellar: normal
Additional features: lower back scar, tuft of hair, bowel/bladder dysfunction
Mononeuropathy, root or plexus lesion
Level: LMN
Distribution: likely unilateral
Sensation: numbness over nerve roots or peripheral nerve
Cerebellar: normal
Additional features: foot drop, wrist drop, claw hand
Mononeuritis multiplex
Level: LMN
Distribution: patchy, asymmetry over multiple peripheral nerves
Sensation: Numbness distributed patchy and asymmetry
Cerebellar: normal
Additional features: DM
What are the common causes of peripheral neuropathy?
- HSMN / CMT
- DM, B12 deficiency, hypo/hyperthyroidism, uraemia, acromegaly
- Alcohol and drugs, heavy metal poisioning
- GBS, CIDP and Sjogren’s syndrome
- Infective - leprosy, HIV
- Paraneoplastic (anti-Hu)
- Amyloidosis and sarcoidosis
- Critical illness neuropathy
What are the causes of cauda equina lesion?
- Traumatic
- Congenital spinal bifida
- Degenerative - lower disc prolapse
- Neoplasm and abscess
What are the causes of mononeuritis multiplex?
- Autoimmune vasculitis - ANCA, RA, lupus, Sjogren
- DM
- Lyme, HIV, leprosy
- Amyloidosis, sarcoidosis
- Paraneoplastic
