OasisLMS

Abstract
Neuromuscular hyperexcitability disorders often manifest as muscle stiffness, spasms, or cramps. These uncommon disorders may be due to central or peripheral nervous system dysfunctions and be either subacute in onset or chronic. Their diagnosis requires a high index of suspicion and is often delayed. Stiff-person syndrome, the prototype of central hyperexcitability disorders, is an immune-mediated disorder that is often associated with high titer glutamic acid decarboxylase antibodies and is amenable to symptomatic treatment and immunotherapy. Peripheral nerve hyperexcitability syndromes, including Isaacs syndrome and Morvan syndrome, are the most common peripheral nerve disorders associated with muscle stiffness. Their diagnosis is usually confirmed by identifying after-discharges that follow the motor response during motor nerve conduction studies and by neuromyotonic and myokymic discharges on needle electromyography (EMG). They are often associated with voltage-gated potassium channel-complex antibodies, specifically toward contact-associated protein-like 2 protein and, less commonly, against leucine rich glioma inactivated 1 protein. These potassium channelopathies overlap with limbic encephalitis, the second most common autoimmune encephalitis. Myotonic disorders, including myotonia congenita and myotonic dystrophies, are the most common muscle disorders that manifest in muscle stiffness and spasms. Rippling muscle disease (RMD) and Brody disease are extremely rare nonprogressive myopathies associated with electrical silence on needle EMG during muscle stiffness and delayed muscle relaxation. RMD has hereditary and immune-mediated forms. It is due to the loss of calveolin-3 or one of its cavin-supportive rafts in muscle membrane. Brody disease is autosomal recessive myopathy due to defective pumping of calcium from the cytoplasm by sarco(endo)plasmic reticulum Ca2+ adenosine triphosphatase pumps.

Objectives: The objectives of this activity are to: (1) Address the causes of muscle stiffness due to neuromuscular hyperexcitability. (2) Understand the pathophysiology and genetics of neuromuscular hyperexcitability disorders. (3) Know the electrodiagnostic findings in neuromuscular hyperexcitability disorders.

ACCREDITATION STATEMENT
The AANEM is accredited by the American Council for Continuing Medical Education (ACCME) to providing continuing education for physicians. AANEM designates this Journal-based CME activity for a maximum of 1.0 AMA PRA Category 1 Credit™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

The author has received royalties from authoring materials for Springer, Elsevier, and Oxford University Press. The editor served as a consultant for Biogen and Insmed. All relevant financial relationships have been mitigated according to Accreditation Council for Continuing Medical Education standards.