Variants and Differential Diagnosis of Peripheral Nerve Hyperexcitability

Aims: Peripheral nerve hyperexcitability syndromes (PNHS) are a heterogeneous group of diseases characterized by spontaneous muscle fiber activity, e.g. myokymias and fasciculations. Acquired, hereditary and idiopathic forms are known. Antibodies to voltage-gated potassium channels (VGKCs) appear likely to be the main effector mechanism in many patients with acquired PNHS. Neuromyotonia (Isaacs' syndrome when acquired), cramp-fasciculation syndrome and Morvan's disease are phenotypic variants of PNHS. Beside of idiopathic forms the association of PNHS and autoimmune diseases is well known. Furthermore medication with penicillamin and clofibrat, hypocalcemia and paraneoplastic autoantibodies can cause PNHS. Symptomatic therapeutical strategies are membrane stabilisation, whereas plasmapheresis and immunosuppression can be indicated in autoimmune forms.

Objectives: Because of the different therapeutical approaches due to the underlying mechanisms of peripheral nerve hyperexcitability, the knowledge about the phenomenology is essential. We describe variants and differential diagnosis of PNHS.

Methods: On the basis of clinical examples we describe main clinical characteristics, pathophysiological concepts and differential diagnostic aspects of PNHS. Furthermore, an overview of the literature and therapeutical strategies will be given.

Results: We described the clinical phenotype, characteristic electrophysiological features and laboratory findings of 5 patients suffering from spontanous muscle fiber activity. Among them there were 2 patients with an acquired and 2 with idiopathic PNHS, one patient suffered from ALS.

Conclusion: The knowledge of the clinical picture and the typical electrophysiological features of PNHS are essential to rule out differential diagnoses like ALS. Whereas in autoimmune and paraneoplastic forms the therapy should be focused on the underlying disease, membrane stabilisation should be performed in idiopatic forms.