Peripheral nerve hyperexcitability

Clinic

38 patients were included.

1. Axonopathic-PNH (12 patients),
2. Isolated nonparaneoplastic PNH (16 patients)
3. Isolated paraneoplastic PNH (3 with thymoma and myasthenia gravis, 1 with thyroid carcinoma)

• PNH clinical features were similar in groups 1 and 2.
• We found an overall high prevalence of clinical autoimmunity (33% of group 1 and 63% of group 2) and systemic non-neuronal autoantibodies (42% of group 1 and 75% of group 2).
• However, VGKC-Abs were only positive in 2 patients of group 2.
• Ten patients underwent muscle biopsy, which showed inflammatory changes in 2 cases and nonspecific myopathic features in 8.

PNH is a heterogeneous disorder involving the peripheral nerves in patients with a high propensity for developing autoimmunity.

Associated muscle diseases are frequent in the form of myositis, myasthenia gravis, or nonspecific myopathic pathologic findings.

VGKC-Abs were uncommon in this series.

Diagnostic features

Peripheral nerve hyperexcitability syndromes are a group of disorders characterized by

• Muscle stiffness
• Cramps
• Muscle twitches
• Involuntary abnormal electrical activity on needle EMG

DD

PNH syndromes are distinct from

• Disorders of muscle stiffness originating in CNS, such as spasticity and stiff person syndrome
• Muscle disorders such as the myotonias, rippling muscle disease
• Glycogen storage diseases.

Despite the presence of several distinguishing clinical and electrophysiologic features in PNH syndromes, a significant overlap exists among the main three nerve hyperexcitability syndromes:

1. Cramp-fasciculation syndrome
2. Isaacs syndrome
3. Morvan syndrome

To add to the confusion, the medical literature has used multiple terms to describe peripheral nerve hyperexcitability syndromes, including

• Idiopathic generalized myokymia,
• Acquired neuromyotonia,
• Armadillo syndrome,
• Syndrome of continuous muscle fiber activity, and
• Quantal squander.

The electrophysiologic terms, including myokymia, neuromyotonia, continuous muscle fiber activity, continuous motor neuron discharges, and neurotonia, are used interchangeably and in an inconsistent fashion.