Differential Diagnosis in Neurology

Topic 10. Differential Diagnosis of Peripheral Neuropathy

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10.19. Nonvasculitic Ischemic Nerve Injury

Compartment Syndrome

General feature:
- Increased pressure within a closed muscular space
- Nerves are injured by compromise of the vasonervorum which decreases their capillary perfusion
- Normal compartment pressure is usually 0–8 mmHg
- Acute compartment syndromes:
  - Anterior compartment of the leg (most common) in the lower extremity
  - Volar forearm compartment (most common) in the upper extremity
- Chronic compartment syndrome:
  - Overuse and exercise:
    - Often anterior and posterior leg compartment are involved
- Acute compartment syndrome:
  - Incipient as they develop; full blown after they are established
- Crush injury:
  - Multiple compartments are involved or large muscle mass such as the gluteal muscle
  - Systemic manifestations of crush injury:
    - Rhabdomyolysis with myoglobinuria
    - Increased serum K⁺ with cardiac arrhythmia
    - Renal failure
    - Shock
Clinical presentation:
- Acute compartment syndrome:
  - Often occurs hours after the inciting event
  - Pain in the involved compartment
  - Swelling, tenderness, edematous skin
  - Dysfunction of the nerves located within the compartment (anesthesia and paralysis)
  - Distal circulation is spared
- Chronic compartment syndrome:
  - Pain in the compromised compartment:
    - Provoked by exercise and relieved by rest
    - Muscle tenderness
    - Paraesthesias and muscle weakness of the affected nerves
Pathogenesis:
- Acute compartment syndrome:
  - Post ischemic edema (arterial surgery; tourniquets)
  - Immobilization and compression (casts, anesthesia, coma)
  - Hematoma (transfusion, anticoagulants)
  - Fracture and soft tissue (edema, blood)
  - Burns (severe edema)
- Chronic compartment syndrome:
  - Exertion or overuse
Pressure measurements of the compartment:
- 30–45 mmHg may be critical
- 10–40 mmHg may be within diastolic pressure
- Arteriogram
- Doppler blood flow evaluation
Differential diagnosis of compartment syndrome:
- Acute compartment syndrome:
  - Primary arterial injury
  - Fracture with nerve injury
  - Cellulitis
  - Venous thrombosis (particularly with clotting disorders if in forearm)
  - Snake bit (common in upper and lower extremity)
  - CRPS I/II
- Chronic compartment syndrome:
  - Vascular claudication
  - Tendonitis
  - Periostitis
  - Fractures
  - Lower extremity:
    - Shin splints (periosteal blood)
    - Fasciitis (high eosinophil count; tenderness and swelling after exercise)
    - Tenosynovitis of the anterior tibial or peroneal muscles
  - Upper extremity:
    - Cardiac pain

Ischemic Monomelic Neuropathy

General features:
- Distal nerve damage in an extremity due to proximal compromise of the arterial supply;
  - Compression of the vessel
  - Diversion of blood
- Occurs in upper and lower extremities
- Distal to proximal gradient of clinical and EMG deficits
- At any limb level different peripheral nerves are affected uniformity
Clinical presentation:
- Deep burning pain in the hand or foot
- Coexisting paresthesias (different nerve distributions)
- The upper extremity has greater distal sensory deficits than the lower extremity
- Weakness and wasting of intrinsic hand and foot muscles; distal > proximal
- Symptoms appear acutely; reach maximum intensity in days
- Impairment of all sensory modalities; distal > proximal; no sensory changes to mid forearm or mid leg
- Rare signs of vascular insufficiency
Pathogenesis:
- A-V shunts in the antecubital fossa or proximal arm for dialysis
- Lower extremity arterial compromise:
  - Superficial femoral artery:
    - cardiopulmonary bypass cannulation
    - Intra-aortic balloon pump
  - Iliofemoral thrombosis
  - Aortoiliac embolus
  - Ergotamine poisoning; methylsurgicide
- Sudden decrease of blood flow to the distal limb
- Nerve pathology:
  - Axonal loss distal to proximal
EMG:
- NCV, sensory and motor responses low in amplitude; sensory > motor
- Fibrillation and decreased MUAP in intrinsic hand and foot muscles
- No concomitant myopathic changes
Differential diagnosis of ischemic monomelic neuropathy:
- Compressive neuropathy (anesthesia positioning)
- Radiculopathy (L4, L5)
- Intermittent claudication
- Plexopathy from axillary block
- Steal syndrome (venous sink):
  - A-V shunt; reversal of distal arterial flow:
    - Non-healing wounds; tissue loss
  - Neurologic dysfunction with no ischemic damage

Acute Ischemic Mononeuropathy and Plexopathy

General features:
- Vasculitis and acute compartment syndrome are the most common causes
- Large vessel atherosclerotic occlusion:
  - Injured during repair
- Lower extremity nerves and the lumbosacral plexus may be involved concomitantly
Clinical presentation:
- Abrupt weakness and sensory loss after reconstructive procedure
- Concomitant signs of vascular insufficiency overshadow neural dysfunction prior to surgery
- Neurogenic claudication:
  - Exercise induced paresthesias of the buttocks and legs (or pain)
  - Weakness of leg muscles with exercise
  - Impotence
Pathogenesis:
- Usual ischemic vessels:
  - Distal aorta (Leriche's syndrome)
  - Internal > external iliac artery
  - Common iliac artery
- Cauda equina and sacral plexus:
  - Blood supply from the internal iliac artery; ilioinguinal artery; Adamkiewicz, great radicular artery whose origin is T12–L1–L2.
- Femoral nerve and lumbosacral plexus most frequently ischemic
- Surgical causes for ischemia:
  - Abdominal aortic iliac surgery:
    - Aneurysms
    - Infected grafts and graft failure
  - Atherosclerotic distal aorta or iliac artery stenosis
  - Pelvic radiation
  - Intra-aortic balloon pumps
  - Intra-arterial injection into the iliac or gluteal arteries
- Nerve fiber ischemia:
  - Hypotension
  - Emboli
  - Inadequate heparinization
  - Cross clamping the aorta or major vessels
- Rare sciatic and common peroneal neuropathies:
  - Ischemia of the common iliac artery
Differential Diagnosis of acute ischemic mononeuropathy/plexopathy:
- Cauda equina lesions
- Conus medullary lesions (bowel/bladder involved; no pain)
- Ischemic femoral neuropathy:
  - Psoas and iliacus anterior compartment syndrome
- Sciatic neuropathy:
  - Incomplete cauda equina lesions
  - Sacral plexopathy
  - Ischemic monomelic neuropathy
Differential features:
- Lumbosacral plexopathy:
  - Unilateral
  - Bladder involvement occurs
  - Motor and sensory loss is in the distribution of more than one nerve
  - Buttock pain occurs first with ischemic lumbosacral plexopathy
- Ischemic femoral neuropathy:
  - Quadriceps weakness
  - Saphenous medial (lower leg paresthesias)
  - Femoral nerve sensory loss
  - Depressed knee jerk
- Iliacus acute compartment syndrome:
  - Groin mass
  - Pain with hip flexion
- Ischemic sciatic neuropathy:
  - Present in distribution of the common peroneal and tibial nerve
  - Weakness/sensory loss below the knee
  - Hamstring, lumbosacral, paraspinal muscles, glutei are normal

Chronic Limb Ischemia

General features:
- May involves both upper and lower extremities
- Caused by peripheral atherosclerotic disease
Clinical presentation:
- Not stereotyped
- Asymptomatic to persistent rest pain; intermittent claudication
EMG:
- Conflicting evidence
- Denervation of affected muscles by needle studies

Frostbite

General features:
- Tissue injury from temperatures below the freezing point of intact skin
- Men > women, 10:1; adult men 30–49 years of age
- High incidence in psychiatric patients
- Feet are involved in more than 90% of patients; less often ears, nose, cheeks and penis
Clinical presentation:
- Exposure occurs in:
  - Homeless patients
  - Psychiatric illness
  - Trauma
  - Outdoor activities
- Direct injury phase:
  - Prior to freezing:
    - Skin temperature less than 10°C
    - Microvascular vasoconstriction with endothelial extravasation
  - Freezing phase:
    - Skin temperature at 2°C
    - Ice crystals in the extracellular fluid causes increased osmotic pressure
    - Intracellular shrinkage; disruption of membrane lipid complexes
    - Cells die an osmotic death when they lose 1/3 of their volume
- Indirect phase during thawing:
  - Vascular stasis with progressive ischemia
  - Tissue destruction occurs during this phase
  - Occurs during first few hours after tissues are rewarmed
  - Microvascular destruction:
    - Affects venules prior to arterioles
  - Release of pro inflammatory mediators such as prostaglandin F₂ and thromboxane A₂
Clinical presentation:
- Pre freeze stage:
  - Loss of light touch, pain and temperature perception
  - Edema
  - Poor coordination of hands and feet
- Freezing stage:
  - Direct injury of frostbite occurs
  - Superficial frostbite:
    - Minimal, if any, tissue loss
    - Supple skin; painful
    - Large blisters with fluid (after thawing)
    - Sensation is intact
  - Deep frostbite:
    - Significant tissue loss
    - Anesthetic tissue
    - Blue grey discoloration
    - Edematous and suffused tissue
    - Hemorrhagic blisters occur with thawing
- Residual symptoms:
  - Burning pain
  - Hyperhidrosis
  - Autonomic dysregulation of the affected part
  - Sensory loss of all modalities
  - Cold intolerance
  - Hyperpigmentation and atrophic skin

Hand-Arm Vibration Syndrome (HAVS)

General features:
- Secondary Raynaud's phenomena
- Sensory dysfunction of the fingers
- Skeletal abnormalities of hand and forearm (X-ray changes)
- Vibrating tools are causative; pneumatic: drills, electric grinders, and polishers, gasoline powered chain saws
- Occurs often after 1000 hours of exposure
Clinical features:
- Numbness and decreased sensitivity of the affected extremity; tip of the fingers are affected first
- Palms not involved
- Specific vasospastic attacks last 1–60 minutes; more common in the morning
- Continued exposure increases the numbers and duration of attacks
- Attacks aborted by warmth; pain and hyperemia occur during warming
- Intrinsic hand muscle atrophy
- Vibration at less than 40 Hz causes wrist and elbow osteoarthritis
- After initial symptoms further exposure causes progressive dysfunction