Differentials
Diabetic lumbosacral radiculoplexus neuropathy
SIGNS / SYMPTOMS
Patients may not have been diagnosed with diabetes mellitus, and may present with weight loss.
Patients have prominent lower extremity proximal pain, with asymmetrical lower extremity proximal weakness more common than distal weakness.[59]
Weakness usually involves both thigh adductors and knee extensors.
Sensory loss is not as prominent as motor weakness, but some evidence of distal length-dependent sensory loss is also present.
INVESTIGATIONS
Electrodiagnostic testing shows evidence of a lumbosacral radiculoplexus neuropathy. Nerve root involvement can often be confirmed and is a typical and distinctive finding.
Serum glucose may or may not be abnormal at presentation, as patients often have lost weight as part of the prodrome and the course of the disorder. HbA1C may be elevated in these cases.
Multiple compression/entrapment mononeuropathies
SIGNS / SYMPTOMS
Usually presentation involves median neuropathy at the wrist (i.e., carpal tunnel syndrome), ulnar mononeuropathy at the elbow, and lateral femoral cutaneous neuropathy (i.e., meralgia paraesthetica).
Patients do not have symptoms or signs involving other organ systems to suggest systemic vasculitis.
Bilateral median neuropathy at the wrist may occur without suspicion for MNM.
Bilateral, painful peroneal mononeuropathies or a unilateral sciatic neuropathy are likely to represent a vasculitic process.
INVESTIGATIONS
Electrophysiological testing helps to show the severity of the entrapment mononeuropathies and the location of the entrapment, and suggests a diagnosis.
There is often demyelination of the nerve at the site of entrapment, which is not consistent with a typical vasculitic MNM.[1]
Hereditary neuropathy with liability to pressure palsies
SIGNS / SYMPTOMS
Presents with episodic, painless, recurrent mononeuropathies from minimal compression (e.g., peroneal mononeuropathy with pronounced foot drop and sensory deficit in the dorsal foot and lateral calf after 20 minutes of kneeling).
Patients do not have symptoms or signs involving other organ systems to suggest a systemic vasculitis.
Affected nerves often recover within a few days or weeks, consistent with a demyelinating lesion of the nerve, differentiating from longer recovery periods associated with axonal neuropathy secondary to vasculitis or other causes.
INVESTIGATIONS
Electrophysiological testing shows generalised, mildly prolonged distal motor latencies and typically conduction block at the site of entrapment mononeuropathy.
Positive genetic testing for PMP22 deletion or point mutation confirms the diagnosis.[1]
Focal and multifocal sensorimotor demyelinating neuropathy (CIDP variant, Lewis-Sumner syndrome)
SIGNS / SYMPTOMS
Typically presents with numbness and paraesthesia within the territories of single nerves of the upper extremities, resulting in progressive weakness and atrophy.
Patients do not have symptoms or signs involving other organ systems to suggest a systemic vasculitis.
The chronic, slow progressive course and upper extremity involvement differentiate this disorder from a typical vasculitic MNM.
INVESTIGATIONS
Electrodiagnostic testing shows motor and sensory conduction block in the affected nerves, often even if the deficits have been present for years.
Peripheral nerve demyelination is not consistent with typical vasculitic MNM.[24]
Multifocal motor neuropathy with conduction block
SIGNS / SYMPTOMS
Presents with pure motor findings, with muscle weakness, fasciculations, and decreased reflexes in the territory of the involved nerves.
Weakness is asymmetrical and upper extremity weakness predominates, typically without pain.
Patients do not have symptoms or signs involving other organ systems to suggest a systemic vasculitis.
The lack of sensory findings and upper extremity predominance differentiates from a typical vasculitic MNM.
INVESTIGATIONS
Electrodiagnostic testing shows motor conduction block in the affected nerves.
Peripheral nerve demyelination is not consistent with typical vasculitic MNM.
Multifocal motor neuropathy without conduction block
SIGNS / SYMPTOMS
Patient presentation is similar to patients with multifocal motor neuropathy with conduction block.
INVESTIGATIONS
Electrodiagnostic testing shows motor neuropathy without evidence of involvement of sensory nerves. Conduction block is not found, distinguishing this from multifocal motor neuropathy with conduction block.
Guillain-Barre syndrome
SIGNS / SYMPTOMS
May present asymmetrically, but deficits are usually not within the distribution of specific nerves.
Patients do not have symptoms or signs involving other organ systems to suggest a systemic vasculitis.
INVESTIGATIONS
Electrodiagnostic studies may show early absence of F-waves or evidence of peripheral nerve demyelination.
Chronic inflammatory demyelinating polyneuropathy (CIDP)
SIGNS / SYMPTOMS
Differentiated from vasculitic MNM by the fact that motor and sensory symptoms typically develop insidiously over weeks to months; motor weakness is both proximal and distal and often symmetric, and not within the distribution of specific peripheral nerves. Patients do not have symptoms or signs involving other organ systems to suggest a systemic vasculitis.
INVESTIGATIONS
Electrodiagnostic testing shows a demyelinating acquired peripheral polyneuropathy.
Peripheral nerve demyelination is not consistent with a typical vasculitic MNM.
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