Continuous muscle fibre activity (Isaacs' syndrome) in infancy: a report of two cases

Neonatal hypertonia - a diagnostic challenge

In comparison to hypotonia, hypertonia is less commonly expressed in the neonatal period. The scientific literature on the causes of neonatal hypertonia is scant, with no suggested diagnostic algorithm easily available to clinicians. Aetiologies include conditions affecting the central nervous system and spine, and rare peripheral neuromuscular disorders leading to hypertonia. Aetiology onset may be antepartum, peripartum with either transient hypertonia or persistent hypertonia which may appear later, or from a postnatal event/disease. This review discusses neonatal hypertonia and a diagnostic approach to neonatal hypertonia is suggested.

Neuromyotonia

Neuromyotonia is a rare condition of spontaneous and continuous muscle fibre activity of peripheral nerve origin. It represents the more severe phenotype of peripheral nerve hyperexcitability, and when acquired is often associated with antibodies to voltage-gated potassium channels. There are no specific published electromyographic or clinical diagnostic criteria for this disorder. This review highlights the classical clinical, electrophysiological and immunological features of this disorder from what is currently known in the literature to date, and also from the author's own patients' studies. Neuromyotonia is best classified as a moderately severe disorder of peripheral nerve hyperexcitability, with electromyographic features of spontaneous, continuous, irregularly occurring doublet, or multiplet single motor unit (or partial motor unit) discharges, firing at a high intraburst frequency (30-300Hz). Invariably, patients develop persistent muscle contraction, often worse following exercise. About 40% of patients with acquired neuromyotonia will have detectable voltage-gated potassium-channel antibodies. Clinical, electrophysiological and immunological measurements are important in defining the phenotype of neuromyotonia, and other, milder forms of peripheral nerve hyperexcitability.

Sporadic major hyperekplexia in neonates and infants: clinical manifestations and outcome

The aim of the present study is to report on the syndrome of sporadic major hyperekplexia during the neonatal period and early infancy, diagnosed in 39 patients at an average age of 3.3 months, the most severely affected during the first month of life. The patients mainly presented with marked irritability and recurrent startles in response to handling or even minute sounds, accompanied by rhythmic jerky movements and occasionally breath-holding episodes. Family history was negative for hyperekplexia, although eight parents reported jerky leg movements during sleep. The hallmark of hyperekplexia consisted of a hyper-alert gaze and an exaggerated startle with delayed habituation, also elicited by nose tapping and air blowing on the face accompanied by increasing rigidity. Nine severely affected infants, presenting with relentless startles, marked stiffness, violent rhythmic jerks, and breath-holding episodes were treated with oral low doses of clonazepam and completely recovered. Overall, the debilitating symptoms of hyperekplexia gradually resolved in all 39 infants, and their developmental assessment by 2 years of age was within the normal range. Therefore a prompt diagnosis of hyperekplexia during the neonatal period and early infancy, and then treatment if required with benzodiazepines to alleviate the debilitating symptoms, may prevent life-threatening events and enable better feeding and handling. Establishing the diagnosis of such a relatively benign disorder with a favorable developmental outcome may avoid unjustified extensive investigations or unnecessary treatment, suspecting an ominous progressive neurologic disorder.

[Isaacs' syndrome. Report of three cases]

We report two females, and one male with Isaacs' syndrome. The patients presented with clinical myokymia activity, muscle cramps, delayed relaxation, and muscle hypertrophy and increased sweating. Needle electromyography in several muscles showed generalized continuous motor unit discharges, myokymic discharges, and normal nerve conduction studies. Muscle biopsy showed type two fiber atrophy. Treatment with carbamazepine was effective in two cases and prednisone in one.