Thyrotoxic encephalopathy and recurrent seizures

Thyroid disease and the nervous system

Thyroid disorders are common in the general population and in hospitalized patients. Thyroid disease may present first with neurological complications or else may occur concurrently in patients suffering other neurological disorders, particularly those with an autoimmune etiology. For this reason neurologists will commonly encounter patients with thyroid disease. This chapter provides an overview of the neurological complications and associations of disorders of the thyroid gland. Particular emphasis is placed on conditions such as thyrotoxic periodic paralysis and myxedema coma in which the underlying thyroid disorder may be occult leading to a first, often emergency, presentation to a neurologist. Information about clinical features, diagnosis, pathogenesis, therapy, and prognosis is provided. Emphasis is placed on those aspects most likely to be relevant to the practicing neurologist and the interested reader is directed to references to good, recent review articles for further information.

Hashimoto's encephalopathy in children and adolescents

Hashimoto's encephalopathy is an underdiagnosed, steroid-responsive, progressive or relapsing encephalopathy associated with high titers of serum antithyroid antibodies. Although Hashimoto's encephalopathy is well documented in adults, it is rarely observed or studied in children and adolescents. We describe the clinical and laboratory findings of four children (aged 9-15 years) with Hashimoto's encephalopathy. The clinical features of two patients at presentation included epileptic seizures and confusion. The other presenting signs included breath-holding spells, behavioral problems, psychosis, and ataxia (one patient each). During their presentation, three patients were euthyroid, and one was hyperthyroid. All patients manifested increased antithyroid antibodies, and all improved with steroid treatment. Hashimoto's encephalopathy is rarely suspected at presentation. Therefore, greater awareness of its signs by clinicians is necessary for proper diagnoses.

The prevalence of thyrotoxicosis-related seizures

BACKGROUND

Central nervous system dysfunction, such as hyperexcitation, irritability, and disturbance of consciousness, may occur in patients with thyrotoxicosis. There are also a few case reports of seizures attributed to thyrotoxicosis. The objective of the present study was to determine the prevalence of seizures that appeared to be related to the thyrotoxic state in patients with thyrotoxicosis.

METHODS

We retrospectively determined the prevalence and clinical features of seizures in 3382 patients with hyperthyroidism. Among patients with seizures, we excluded those with other causes of seizures or a history of epilepsy. We did not exclude two patients in whom later work-up showed an abnormal magnetic resonance imaging, as their seizures resolved after they became euthyroid.

RESULTS

Among the 3382 patients with hyperthyroidism, there were seven patients (0.2%) with seizures who met our criteria. Primary generalized tonic-clonic seizures occurred in four patients (57%), complex partial seizures with secondary generalized tonic-clonic seizures occurred in two patients (29%), and one patient had a focal seizure (14%). The initial electroencephalography (EEG) was normal in two patients (29%), had generalized slow activity in four patients (57%), and had diffuse generalized beta activity in one patient (14%). On magnetic resonance imaging, one patient had diffuse brain atrophy, and one had an old basal ganglia infarct. After the patients became euthyroid, the EEG was repeated and was normal in all patients. During follow-up periods ranging from 18 to 24 months, none of the patients had seizures.

CONCLUSIONS

Hyperthyroidism is the precipitating cause of seizures in a small percentage of these patients. In these patients, the prognosis is good if they become euthyroid. The prevalence of thyrotoxicosis-related seizures reported here can be used in conjunction with the prevalence of thyrotoxicosis in the population to estimate the prevalence of thyrotoxicosis-related seizures in populations.

Concurrent Graves disease thyrotoxicosis and myasthenia gravis: the treatment of the former may dangerously reveal the latter

Autoimmune thyroxicosis and myasthenia gravis are often associated. In both diseases, clinical features may include neuromuscular weakness, making their distinction challenging. We report a patient with known Graves disease who presented with generalised fatigue, initially attributed solely to thyrotoxicosis, and who experienced severe respiratory failure linked to associated myasthenia gravis that was unmasked by medication used in the perioperative management of his thyroxicosis. Anaesthetists should always consider myasthenia gravis in cases of hyperthyroidism presenting with neuromuscular features.

Significance of atypical triphasic waves for diagnosing nonconvulsive status epilepticus

The aim of the study described here was to analyze findings in 15 cases who were admitted with nonconvulsive status epilepticus (NCSE) and whose EEGs featured atypical triphasic waves (ATWs). We also investigated whether ATWs are useful for diagnosing this condition. Mental status was assessed, and EEGs were recorded during/after the antiepileptic drug treatment. Eight patients had metabolic disorders and nine had intracranial pathology. The ATWs were unilateral focal in 5 cases and bilaterally asymmetrical focal in 10 cases. In 11 of the 15 cases, the ATWs disappeared and mental status improved after treatment. NCSE should be considered in any individual who presents in an acute confusional state and whose EEG reveals either unilateral or bilaterally asymmetric ATWs.

Neuromuscular complications of thyrotoxicosis

Thyroid hormones exert multiple effects on the neuromuscular system and the brain, with the most important being their role in stimulating the development and differentiation of the neuromuscular system and brain in foetal and neonatal life. In the presence of hyperthyroidism, muscular and neurological symptoms may be the presenting clinical features of the disease. The frequency and severity of neuromuscular complications vary considerably and are probably related to the degree of hyperthyroidism, although in some patients the neuromuscular dysfunction is caused by associated disorders rather than by hyperthyroidism per se. This update focuses on the most common neurological and muscular disorders that occur in patients with thyrotoxicosis. It is beyond the scope of this paper to discuss thyroid eye disease and cardiac complications, in themselves separate complications of specific myocytes.

Thyrotoxic autoimmune encephalopathy in a female patient: Only partial response to typical immunosuppressant treatment and remission after thyroidectomy

Hashimoto's encephalopathy (HE) is a rare immune-mediated encephalopathy developing in patients with high serum concentrations of anti-thyroid antibodies usually in an euthyroid or hypothyroid state. We report a 31-year-old female patient with thyrotoxic HE whose daughter has been followed up with the same diagnosis. Suboptimal response was observed with intravenous methylprednisolone (IVMP), intravenous immunoglobulin (IVIG) and plasmapheresis. Reduction of the anti-thyroid auto-antibody concentrations marked the patient's improvement in each episode. She relapsed under oral immunosuppressive therapy. After removing the thyroid tissue, full recovery has been achieved for the last 18 months. These data may contribute to clarification of the pathogenetic role of anti-thyroid antibodies in HE. Thyroidectomy can be considered as one of the treatment options especially in thyrotoxic HE patients with uncontrolled relapses. Our patient is the first reported HE case with a family history. Genetic background can underlie the etiopathogenesis of HE as is the case in other autoimmune disorders.

Interictal EEG and the diagnosis of epilepsy

The interictal EEG provides information that aids in diagnosis and management of epilepsy. One must remember that the EEG is merely a tool, and its usefulness depends largely upon the skill of the individual who wields it. Like all diagnostic tests, it has significant limitations and cannot substitute for a careful history and exercise of good judgment. Nonetheless, in skilled hands, it provides unique and vital information in many patients, and enhances our understanding of their condition.

Hashimoto's myoclonic encephalopathy: an underdiagnosed treatable condition?

We report two patients with subacute diffuse encephalopathy characterized by confusion, myoclonic encephalopathy, and mild akineto-rigid extrapyramidal signs in one case and by apathy, memory deficit, and partial complex seizures in the other. Hashimoto's thyroiditis with high titers of anti-thyroglobulin antibodies was diagnosed in both patients, who were unresponsive to anticonvulsant medication, but showed rapid neurological improvement following steroid treatment. On neuropsychological examination, predominant frontotemporal dysfunction was noted. Electroencephalographic activity was remarkable for its rhythmical delta activity, unresponsive to, or even paradoxically increased by, anticonvulsant treatment. On magnetic resonance imaging, atrophy with temporal predominance was found. These observations support the idea that this potentially treatable dementia and movement disorder should be classified as a separate clinical entity.

Neurologic complications of thyroid and parathyroid disease

Common thyroid and parathyroid disorders present with reversible neurologic signs and symptoms affecting the central and peripheral nervous system, musculature, and mental function. Patients with thyrotoxicosis may have myopathy, spasticity, seizures, and multiple psychiatric symptoms. A deficiency of thyroid hormone also causes muscle weakness and may be accompanied by reversible muscle hypertrophy or movement disorders. The chronic hypercalcemia that develops secondary to hyperparathyroidism produces many psychiatric and cognitive symptoms, as well as a reversible myopathy. Calcium deficiency leads to neuromuscular irritability, paresthesias, and tetany. Psychiatric disorders are also common in this disorder.