Hypothyroid neuropathy and myopathy: clinical and electrodiagnostic longitudinal findings

Hoffmann's syndrome in the differential work-up of myopathic complaints: a case report

BACKGROUND

Hoffmann's syndrome is a rare form of hypothyroid myopathy in adults, which is mainly characterized by muscular weakness and muscular pseudohypertrophy.

CASE PRESENTATION

We report about a 61-year-old Western European man with myalgia, myxedema and pseudohypertrophy of the calf muscles. Laboratory tests revealed significantly elevated thyroid stimulating hormone (TSH) and creatine kinase (CK). Muscle MRI showed muscular hypertrophy of the lower limbs, but no signs of myositis or myopathy (no gadolinium enhancement, no edema, no fatty degeneration). In addition, electromyography (EMG) detected spontaneous activity. After the beginning of thyroxin-therapy it took six months until the muscle weakness improved and the myalgia regressed.

CONCLUSIONS

Here, we focus on diagnostic routines and typical findings to differentiate Hoffmann's syndrome from other myopathies. Clinical hallmarks of Hoffmann's syndrome are pseudohypertrophy and weakness of the calf muscles in combination with elevated CK and elevated TSH. EMG is well suited to detect the involvement of the muscles and muscle MRI helps to differentiate it from other myopathies. Hoffmann's syndrome is a rare myopathy due to hypothyroidism and plays a role in the differential diagnosis of myopathic complaints even if hypothyroidism has not been detected before.

Sympathetic skin responses and electromyographic reaction times in chronic autoimmune thyroiditis: An overlooked electrodiagnostic study

Objectives

This study aims to evaluate peripheral nerve functions, sympathetic skin responses (SSRs), and electromyographic (EMG) reaction times in hypothyroid patients and to compare them to healthy individuals.

Patients and methods

Between January 2007 and September 2007, a total of 54 patients with Hashimoto’s thyroiditis including 35 euthyroid (3 males, 32 females; mean age: 45.2±10.2 years; range, 35 to 60 years) and 19 with subclinical hypothyroidism (2 males, 17 females; mean age: 43.2±12.6 years; range, 40 to 65 years) were included in the study. The control group consisted of 35 healthy individuals (5 males, 30 females; mean age: 39.1±9.3 years; range, 29 to 52 years). Nerve conduction studies (NCSs), SSRs of the hand and foot obtained by stimulation of the contralateral median nerve, and EMG reaction times of the extensor indicis proprius muscle were performed in all subjects.

Results

There was no significant difference in peripheral NCSs and SSRs between patients and the control group. However, reaction times were longer in the AIT patients compared to the healthy individuals suggesting alterations in cognitive function related to the primary disease process in AIT.

Conclusion

Electrodiagnosis of autonomic nervous system involvement and cognitive impairment can be challenging in AIT. However, EMG reaction times and SSRs are practical and useful tools that are often overlooked. On the other hand, SSRs may be combined with more quantitative tests, such as sudomotor axon reflex testing, to allow us to better determine the extent of involvement of the autonomic nervous system in AIT.

Severe Hypothyroidism Complicated by Myopathy and Neuropathy with Atypical Demyelinating Features

Autoimmune hypothyroidism may result in a wide range of neuromuscular disorders. The frequently observed neurological manifestations of acquired hypothyroidism include mild to moderate myopathy and sensorimotor neuropathy, which usually resolve by clinical and electrophysiological criteria, in adults treated with thyroid hormone replacement. We report a case of a 30-year-old male with severe hypothyroidism secondary to chronic autoimmune thyroiditis who presented with a 2-year history of progressive fatigue, upper and lower limb weakness, myalgia, and intermittent paraesthesia. His neurological exam demonstrated proximal and distal muscle weakness, lower limb areflexia, and relatively intact sensory modalities. The patient's biochemistry revealed unusually and profoundly raised the thyroid stimulating hormone (TSH) level of 405.5 mIU/L (reference range (RR): 0.27–4.2 mIU/L) and creatine kinase (CK) level of 20,804 U/L (RR: 45–250 U/L), while his nerve conduction studies (NCS) demonstrated severe sensorimotor polyneuropathy with both axonal and demyelinating features. Thyroid hormone replacement therapy over the first 3 months resulted in biochemical normalization of his extremely deranged thyroid function tests (TFTs) and CK levels. At 12 months, despite maintaining euthyroidism and noticeable improvement in strength, his nerve conduction studies (NCS) demonstrated the continued absence of distal motor and sensory responses in his lower limbs with only partial improvement in sensory amplitudes and conduction velocities in his upper limbs. This report highlights the potential for severe neuromuscular consequences from advanced and chronic autoimmune hypothyroidism. The patient's myopathy has resolved over a period of three months with prompt normalization of CK levels. Concerningly, the patient achieved significant but incomplete recovery from his mixed axonal and demyelinating neuropathy with residual mild distal weakness and areflexia in his lower limbs and persistent motor and sensory impairments on his NCS. The severity and incomplete resolution of our patient's neurological manifestations emphasize the importance of early diagnosis and the need for prompt therapeutic intervention for hypothyroidism.

Allan-Herndon-Dudley-Syndrome: Considerations about the Brain Phenotype with Implications for Treatment Strategies

Despite its first description more than 75 years ago, effective treatment for "Allan-Herndon-Dudley-Syndrome (AHDS)", an X-linked thyroid hormone transporter defect, is unavailable. Mutations in the SLC16A2 gene have been discovered to be causative for AHDS in 2004, but a comprehensive understanding of the function of the encoded protein, monocarboxylate transporter 8 (MCT8), is incomplete. Patients with AHDS suffer from neurodevelopmental delay, as well as extrapyramidal (dystonia, chorea, athetosis), pyramidal (spasticity), and cerebellar symptoms (ataxia). This suggests an affection of the pyramidal tracts, basal ganglia, and cerebellum, most likely already during fetal brain development. The function of other brain areas relevant for mood, behavior, and vigilance seems to be intact. An optimal treatment strategy should thus aim to deliver T3 to these relevant structures at the correct time points during development. A potential therapeutic strategy meeting these needs might be the delivery of T3 via a "Trojan horse mechanism" by which T3 is delivered into target cells by a thyroid hormone transporter independent T3 internalization.

Hoffmann's Syndrome Secondary to Pendred Syndrome: A Rare Case

Hoffmann's syndrome (HS) is a rare manifestation of hypothyroidism myopathy that presents with weakness, stiffness, and eventually pseudohypertrophy of muscles, especially calf muscles. We report a case of a 28-year-old male who presented with the history of generalized weakness with swelling in lower limbs and gradual progressive facial puffiness for the past few years. Physical examination of our patient showed diffuse bilateral pseudohypertrophy of deltoid and calf muscles with positive Gowers' sign (GS). Laboratory results of low serum thyroid hormones and muscle biopsy report confirmed the diagnosis of HS. Pendred syndrome (PS) is a genetic disorder leading to congenital bilateral sensorineural hearing loss with mild hypothyroidism. On account of his congenital bilateral sensorineural hearing loss and negative serum anti-thyroid peroxidase antibodies (anti-TPO Ab), PS was declared as the cause of HS in this case. Our patient showed excellent response to levothyroxine therapy with progressive improvement in his symptoms. We outlined this case due to its rarity.

Hypothyroid myopathy: A peculiar clinical presentation of thyroid failure. Review of the literature

Abnormalities in thyroid function are common endocrine disorders that affect 5-10 % of the general population, with hypothyroidism occurring more frequently than hyperthyroidism. Clinical symptoms and signs are often nonspecific, particularly in hypothyroidism. Muscular symptoms (stiffness, myalgias, cramps, easy fatigability) are mentioned by the majority of patients with frank hypothyroidism. Often underestimated is the fact that muscle symptoms may represent the predominant or the only clinical manifestation of hypothyroidism, raising the issue of a differential diagnosis with other causes of myopathy, which sometimes can be difficult. Elevated serum creatine kinase, which not necessarily correlates with the severity of the myopathic symptoms, is certainly suggestive of muscle impairment, though it does not explain the cause. Rare muscular manifestations, associated with hypothyroidism, are rhabdomyolysis, acute compartment syndrome, Hoffman's syndrome and Kocher-Debré-Sémélaigne syndrome. Though the pathogenesis of hypothyroid myopathy is not entirely known, proposed mechanisms include altered glycogenolytic and oxidative metabolism, altered expression of contractile proteins, and neuro-mediated damage. Correlation studies of haplotype, muscle gene expression and protein characterization, could help understanding the pathophysiological mechanisms of this myopathic presentation of hypothyroidism.

Hoffmann's syndrome with unusually long duration: Report on clinical, laboratory and muscle imaging findings in two cases

Two adult men presented with the rare Hoffmann's syndrome (HS). Case 1: A 35-year-old male patient had progressive stiffness of lower limbs of 13 years and generalized muscle hypertrophy and myalgia of 3 years duration. Had periorbital edema, dry skin, generalized muscle hypertrophy and spastic dysarthria with hoarseness. Muscle power was normal. Jaw jerk and deep tendon reflexes were exaggerated. Case 2: A 24-year-old male patient presented with muscle hypertrophy from childhood, slowness in motor activities and hearing impairment. For 6 months, he had severe muscle pains, cramps and further increase in hypertrophy. He had yellow tinged, dry skin, hoarseness of voice, gross muscle hypertrophy and minimal weakness. Both had markedly elevated serum creatine kinase (CK) levels and high thyroid stimulating hormone, low free triiodothyronine and free thyroxine levels. Levothyroxine treatment demonstrated remarkable reduction in muscle bulk at 2 months in both and no symptoms at 6 months. Magnetic resonance imaging of lower limbs in both cases revealed almost identical features with involvement of the muscles of posterior and adductor compartment of thighs and posterior and lateral compartments of the legs. Differential diagnosis of long duration muscle pseudohypertrophy and elevated CK levels should include HS.

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.

A community-based epidemiological study of peripheral neuropathies in Assiut, Egypt

BACKGROUND

There is very little published information about the prevalence, patterns, and predictors of peripheral neuropathies. The current study is a community-based survey was conducted in the Assiut Governorate to estimate their prevalence and clinical profile.

MATERIAL AND METHODS

A door-to-door study was carried out on 42,223 persons from rural and urban communities in the Assiut Governorate, Egypt. There were 13,288 (31.5%) subjects from the urban and 28,935 (68·5%) from the rural area. All subjects filled in a questionnaire designed specifically for diagnosis of peripheral neuropathy. Positive cases were then given a complete medical and neurological examination, routine laboratory tests, neurophysiology, and neuroimaging (magnetic resonance).

RESULTS

The crude prevalence rate (CPR) of peripheral neuropathy was 3181/100,000 inhabitants. There was a significantly higher prevalence in the rural compared with the urban population (3795 versus 1844/100,000) and in females than males (4473 versus 1943/100,000; P<0.001 for both). The most common type reported was entrapment neuropathy (736 cases with CPR of 1743/100,000), particularly carpal tunnel syndrome (1686/100,000). Diabetic neuropathy was the most common non-compressive neuropathy with a CPR of 649/100,000. Type II diabetes was recorded in 241 patients with a CPR of 571/100,000. Compressive radiculopathy had a crude prevalence of 358/100,000; traumatic and iatrogenic radiculopathy had a prevalence rate of 149/100,000. Less common conditions were: uremic neuropathy (21/100,000) hepatic neuropathy (14/100,000), Bell's palsy (28/100,000), Guillian-Barre' syndrome (12/100,000), chronic inflammatory demyelinating polyneuropathy (12/100,000), hereditary sensory motor neuropathy (12/100,000), and idiopathic neuropathy (92/100,000).

CONCLUSION

The overall prevalence of peripheral neuropathies was high in comparison to other studies. Entrapment neuropathy, diabetic neuropathy, and spondylotic radiculopathy were the most common. Overall, the prevalence of peripheral neuropathy was higher in the rural than in the urban population.

Rhabdomyolysis and peroneal nerve compression associated with thyroid hormone withdrawal in the setting of remnant ablation: review of the literature

OBJECTIVE

To review the putative mechanisms whereby hypothyroidism is associated with severe myopathy, neural injury, and acute compartment syndrome and report a case of nontraumatic common peroneal nerve compression associated with hypothyroidism-induced rhabdomyolysis in a patient with diabetes prepared for remnant ablation after thyroidectomy for differentiated thyroid carcinoma.

METHODS

We performed a review of the English-language literature on the PubMed database using the terms hypothyroidism, muscle disease, hypothyroid myopathy, rhabdomyolysis, compression neuropathy, and acute compartment syndrome.

RESULTS

Myopathy occurs frequently among patients with overt hypothyroidism; however, severe myoneural injury seems to be precipitated or accompanied by comorbid conditions. Focal peroneal neuropathy may be related to hypothyroidism-induced extrinsic compression from severe myopathy and soft tissue swelling in a narrowed fascial compartment.

CONCLUSION

Severe short-term iatrogenic hypothyroidism may lead to severe myopathy and compression nerve injury in patients with underlying diabetic neuropathy. We recommend avoidance of withdrawal of thyroid hormone for purposes of remnant ablation among patients with preexisting diabetic neuropathy.

The prevalence of undiagnosed thyroid disease in patients with symptomatic vocal fold paresis

OBJECTIVE

Vocal fold paresis has a multifactorial etiology and is idiopathic in many individuals. The incidence of thyroid-related neuropathy in the larynx has not been previously described. The purpose of this study was to evaluate the prevalence of previously undiagnosed thyroid disease in patients with laryngeal neuropathy and to compare this prevalence with that in a cohort of patients with a neurotologic neuropathy.

STUDY DESIGN AND SETTING

Case series with chart review; tertiary care, otolaryngology practice.

SUBJECTS AND METHODS

Charts of 308 consecutive patients with dysphonia and vocal fold paresis and 333 consecutive patients with sensorineural hearing loss, who presented for evaluation during a 3-year period, were reviewed.

RESULTS

One hundred forty-six of 308 (47.4%) patients with vocal fold paresis were diagnosed with concurrent thyroid disease, whereas 55 of 333 (16.5%) patients with sensorineural hearing loss were diagnosed with concurrent thyroid disease (P<0.001, Pearson chi-square = 92.896; degrees of freedom = 5). Thyroid diagnoses among those with vocal fold paresis included benign growths (29.9%), thyroiditis (7.8%), hyperthyroidism (4.5%), hypothyroidism (3.6%), and thyroid malignancy (1.6%).

CONCLUSIONS

Thyroid abnormalities are more prevalent in patients with dysphonia and vocal fold paresis than in patients with symptomatic sensorineural hearing loss, suggesting a greater association between previously undiagnosed thyroid abnormalities and laryngeal neuropathy than that between neurotologic neuropathy and thyroid disease.

Hypothyroid myopathy with manifestations of Hoffman's syndrome and myasthenia gravis

Although hypothyroid myopathy is seen frequently and the relationship with autoimmune hypothyroidism and myasthenia gravis is well known, specific forms of hypothyroid myopathy such as Hoffman's syndrome (HS) are rarely described. Here we describe a 40-year-old patient with Hashimoto thyroiditis showing symptoms and signs of two discrete forms of hypothyroid myopathy (HS and myasthenic syndrome) together. To our knowledge this is the first reported case with features of both of these syndromes. We discuss the diagnosis, speculate whether this patient may represent a unique form of hypothyroid myopathy, and report the 6-month follow-up of the patient both clinically and electrophysiologically.

Hormone replacement therapy in hypothyroidism and nerve conduction study

OBJECTIVES

To evaluate the electrodiagnostic evidence of peripheral nerve dysfunction in patients with hypothyroidism before and after hormone replacement treatment.

MATERIALS AND METHODS

Forty patients aged above 18 years diagnosed with hypothyroidism were included in our study. Patients with FT4 levels below 11.6 pmol/l and TSH levels above 4.2 IU/ml were accepted as hypothyroidic. Electrodiagnostic evaluation was performed at the onset of the study and after 3 months. Electrodiagnostic evaluation included motor and sensory nerve conduction studies, and F wave.

RESULTS

The differences between pre- and post-treatment FT4, FT3 and TSH values were found to be statistically significant. At the onset, electrophysiological evaluation revealed carpal tunnel syndrome in 15 patients and polyneuropathy in seven patients; whereas 18 patients were found normal in these respects. After treatment, the electrodiagnostic evaluation revealed that 35 patients were normal, while only two patients had carpal tunnel syndrome and three patients had polyneuropathy. The differences between before and after treatment values of median motor distal latency and amplitude, median sensorial nerve conduction velocity, tibial motor nerve conduction velocity and sural sensory nerve conduction velocity were found to be statistically significant.

CONCLUSION

The results of the control evaluation after treatment demonstrated that the findings related to entrapment neuropathy and polyneuropathy in hypothyroid patients can be reversible in a period of 3 months if appropriate hormone replacement treatment can be obtained. Especially in the treatment of entrapment neuropathy in hypothyroidism, the chance of medical treatment must be given to patients before considering surgical treatment.

Hoffman's syndrome: pseudohypertrophic myopathy as initial manifestation of hypothyroidism. Case report

The frequency of myopathy in hypothyroidism ranges from 30 to 80%. The major symptoms related are weakness, muscular cramps and myalgia. The pseudohyperthrophic form is called Hoffman's syndrome. The electrophysiological study reveals myopathy, neuropathy or mixed pattern. Laboratorial investigation generally shows increased levels of muscle enzymes and low serum thyroid hormones, with thyrotrophic-stimulating hormone (TSH) elevated. The treatment consists in hormone replacement and the prognosis is good in most of the cases. We report an adult male who developed muscular cramps, myalgia, weakness, pseudohyperthrophy, associated with facial edema and alteration of his voice. The muscle enzymes were increased and T4 was undetectable with a raised level of TSH. The myopathy was the initial manifestation of hypothyroidism in this case.

EMG myokymia as a cause of ptosis in hypothyroidism

Ptosis is known to be associated with thyroid disorders. We describe two biochemically corrected hypothyroid patients presenting with isolated bilateral ptosis. EMG of the orbicularis oculi showed continuous grouped motor unit potentials. In the absence of obvious aetiology, it is hypothesised that focal demyelination of terminal branches to the orbicularis oculi may play a role in the generation of the discharges.

Hypothyroid myopathy with a strikingly elevated serum creatine kinase level

Although serum creatine kinase (CK) levels are frequently modestly elevated in patients with hypothyroid myopathy, elevations in serum CK to the levels usually seen in inflammatory myopathies or dystrophies are rare. We report a patient with progressive proximal weakness and a serum CK level of over 29,000 IU/L, in whom subsequent laboratory evaluation identified profound hypothyroidism. Thyroid hormone replacement therapy resulted in resolution of clinical symptoms and a marked reduction in the serum CK level. Such a high serum CK level in a patient with hypothyroidism underscores the importance of assessing thyroid function in patients with weakness, regardless of serum CK levels, even when systemic symptoms and signs of hypothyroidism are minimal or absent.

Dysarthria as the leading symptom of hypothyroidism

Typical symptoms of hypothyroidism are lethargy, cold intolerance, slowing of intellectual and motor activity, declining appetite, increasing weight, and dry skin. A 43-year-old man with hypothyroidism presented with dysarthria as the leading symptom. Further symptoms were cramps in the legs after exercise, dizziness, and stunned feeling. He suffered from severe snoring for 4 years, and obstructive sleep apnea syndrome was diagnosed 2 years before. Creatine phosphokinase was elevated. Electromyography was myogenic. Echocardiography showed a thickened myocardium. An otolaryngologic investigation revealed macroglossia and hypertrophy of the uvula. After administration of L-thyroxine, the symptoms rapidly improved. Dysarthria may be the leading symptom of hypothyroidism and can be promptly resolved after hormone substitution.

Myopathies in the elderly

Muscle disease symptoms and myopathies are not uncommon in the elderly. Inflammatory and noninflammatory myopathies lead to proximal extremity or axial weakness and are superimposed on the intrinsic changes that occur in muscle with aging (sarcopenia). This article surveys the more common myopathies in the elderly based on a review of the process of sarcopenia, and how these age-related changes in muscle structure and function affect the results of the standard assessments of muscle disease in the elderly.

The effects of hypothyroidism and thyroid replacement on the development of carpal tunnel syndrome

Hypothyroidism is commonly included as an important risk factor for carpal tunnel syndrome (CTS), yet no study clearly defines the nature of this association. The purpose of this study was to evaluate the relationship between hypothyroidism and CTS in a controlled study. Twenty-six hypothyroid patients (45 hands) meeting our inclusion criteria with a diagnosis of primary hypothyroidism were questioned regarding date of diagnosis of hypothyroidism, duration and dose of thyroid replacement, and the presence, character, and duration of CTS symptoms. Twenty-four healthy volunteers (47 hands) were used as controls. Clinical examination included sensibility testing with Semmes-Weinstein monofilaments, Weber 2-point discrimination testing, examining for thenar muscle atrophy and weakness, Phalen's test, Tinel's sign at the wrist, and the manual compression test. Electrodiagnostic testing including distal motor latency and distal sensory latency was performed on the median nerve at the wrist on all subjects. Nineteen patients (73%; 31 hands [68%]) displayed symptoms of CTS; of these, 16 patients (25 hands) had clinical examinations consistent with CTS. Only 6 of the 16 patients with clinical CTS (7 of 25 hands) had electrical studies that supported a diagnosis of CTS. All these symptomatic patients were biochemically euthyroid. All control subjects had normal electrical study results and normal sensibility testing. Two subjects had positive clinical examinations, giving a false-positive rate of 4%. Carpal tunnel syndrome symptoms are common in hypothyroid patients even when they are euthyroid. In this group of patients, normal median nerve latencies at the wrist in the presence of CTS symptoms and a positive physical examination are more prevalent than expected by the reported sensitivities of electrodiagnostic testing. Standards for assessing normal median nerve latencies may be significantly different in hypothyroid patients.

The recovery potential of central conduction disorder in hypothyroid rats

In an aim to detect the dysfunction of central nervous system among rats with varied durations of hypothyroidism and to elucidate the recovery potential after thyroxine replacement, a series of BAEP were conducted and compared with age-matched controls. BAEP was performed in five groups of the hypothyroid animals 1, 3, 5, 7, and 9 months after thyroidectomy respectively. Following initial electrophysiological assessment, thyroxine replacement was administered to each group of hypothyroid rats, and BAEP was performed at two month intervals, up to two successive normal studies or six months after the initiation of therapy, whichever came first. Before thyroxine treatment, prolonged I-V interpeak latency was the most consistent abnormal finding in all groups of hypothyroid rats, and longer hypothyroid state correlated well with more severe central conduction disorder. Hearing impairment was also noted among those with long duration of hypothyroidism. After thyroxine replacement, the central conduction dysfunction usually returned to normal if the hypothyroid state was not more than 5 months in duration. However, when hypothyroid state persisted over 7 months or more, there would be an incomplete recovery for central conduction disorder. The present study brings out the concept of 'therapeutic window' in reversing the central nervous dysfunction caused by hypothyroidism in adult rats.

A longitudinal study of central and peripheral nerve conduction in hypothyroid rats

In order to detect the dysfunction of central and peripheral nervous systems among rats with varied duration of hypothyroidism and to elucidate the pattern of recovery after thyroxine replacement, a series of BAEP and PNCS (Peripheral Nerve Conduction Study) were conducted and compared with age-matched controls. BAEP and PNCS were performed in three groups of hypothyroid animals 1, 3 and 5 months after thyroidectomy, respectively. Following initial electrophysiological assessment, thyroxine replacement was administered to each group of hypothyroid rats, and BAEP and PNCS were performed at two month intervals, up to two successive normal studies, or six months after the initiation of therapy, whichever came first. For BAEP, prolonged I-V interpeak latency was the most consistent abnormal finding in all groups of hypothyroid rats, and longer hypothyroid states correlated well with more severe central conduction disorder. Nevertheless, these abnormalities usually returned to normal after thyroxine replacement if the duration of hypothyroidism was less than 5 months. Regarding PNCS, all groups of thyroidectomized rats showed normal conduction before and after thyroxine therapy. The present study indicates that, in rats: (1) the peripheral nervous system seems to be more resistant to hypothyroidism than the central nervous system, or (2) the pathogenesis of central and peripheral nerve dysfunction in hypothyroid rats may occur through different mechanisms.

Evaluation of central motor conduction in hypothyroid and hyperthyroid patients

Deficiency or excess of thyroid hormones is associated with central nervous system (CNS) disturbances. Although the CNS involvement either in hypothyroidism or in hyperthyroidism have previously been shown on the basis of visual, auditory and somatosensory evoked potentials studies, less is known about the function of central motor pathways in both disorders. We studied the motor evoked potentials (MEPs) following the magnetic stimulation of the motor cortex and spinal roots in 20 patients with hypothyroidism and in 19 patients with hyperthyroidism both before treatment and after they became euthyroid and compared with findings in 20 age-, sex- and height-matched control subjects. Disease duration (expressed as time from diagnosis of diseases to the time of neurological testing) is less than one month in both disorders. Central motor conduction time (CMCT) was determined as the differences between MEPs latencies after cortical and spinal stimulation. The mean CMCTs before treatment in hypothyroid patients (8.31 +/- 1.52 msec.) and in hyperthyroid patients (7.92 +/- 1.06 msec.) were significantly prolonged as compared to those in normal controls (6.82 +/- 0.83 msec. p = 0.002 and p = 0.004, respectively). Four of the 20 (20.0%) hypothyroid patients and 2 of 19 (10.5%) hyperthyroid patients had abnormal CMCT (values exceeding mean +2.5 SD of normal control). The mean CMCT values in both groups were not significantly decreased after euthyroidism was achieved, although a tendency of the decrease in CMCT was observed. Improvement of CMCT abnormalities was observed in 1 of 4 hypothyroid patients and in one of 2 patients with hyperthyroidism, who had CMCT abnormalities before treatments, after they became euthyroid. No correlation was found between CMCT and free T3, free T4, or TSH levels as well as the onset age, the severity of the diseases or the disease duration in both disorders. We conclude that abnormal CMCT could be documented in few patients in both disorders. However, these alterations could not be improved completely after restoration of euthyrodism. Thus, it remains to be determined if long-term treatment would completely improve CMCT abnormalities in both disorders. Since abnormal CMCT values in both disorders were observed only in few patients, our results also suggest that CMCT measurement does not have, at present time, a clinical usefulness to assess the peripheral action of thyroid hormones. Thus, the data obtained need a more extensive evaluation.

Acute hypothyroidism leads to reversible alterations in central nervous system as revealed by somatosensory evoked potentials

Although functional alterations in the central nervous system (CNS) and peripheral nerves are well documented in overt hypothyroidism, little is known about alterations of CNS in acute hypothyroidism. Sixteen patients with differentiated thyroid carcinoma were studied when prepared for radioiodine scanning after stopping levothyroxine (L-T4) therapy for 6 weeks to determine whether acute hypothyroidism leads to alteration in somatosensory evoked potentials (SSEPs). Repeat SSEPs were performed on the same patients at 6 months following L-T4 therapy when patients were euthyroid. Neurophysiological findings were compared with a group of 20 normal controls with no history of thyroid disease. Peripheral and central conduction in the median and tibial nerve stimulated SSEPs studied. A significant prolongation of central conduction time in SSEPs was found in patients with acute hypothyroidism when compared to those in control subjects. Abnormal latencies were not correlated with thyroid hormone levels. These neurophysiologic abnormalities were completely restored to normal at 6 months after L-T4 therapy. We conclude that acute hypothyroidism leads to reversible alterations in CNS as determined by SSEP recordings. Our results also suggest that SSEPs could be useful tests to monitor functional alteration of the CNS in acute hypothyroidism.

Electroneuromyography and neuromuscular findings in 16 primary hypothyroidism patients

There has been few reports on electroneuromyography (ENMG) changes in hypothyroidism. The objectives of the present study were to investigate the frequency of ENMG abnormalities in hypothyroidism and correlate them with neurological signs and symptoms and muscle enzyme levels; and to compare latency, amplitude and nerve conduction velocity from selected nerves with controls. Sixteen patients suffering from primary hypothyroidism were submitted to ENMG before treatment. ENMG abnormalities were found in 87.5% of the patients; 46.6% had myopathy and 43.7% had carpal tunnel syndrome. There was no case of polyneuropathy. A clear-cut clinical, laboratorial and ENMG correlation was observed in patients with myopathy and carpal tunnel syndrome. The patients showed a significant tendency of nerve conduction slowness as compared with controls. The findings are in accordance with the well-known nerve and muscle damage in hypothyroidism.

Subclinical hypothyroidism does not lead to alterations either in peripheral nerves or in brainstem auditory evoked potentials (BAEPs)

Functional alterations in the central nervous system and peripheral nerves are well documented in overt hypothyroidism, but not in subclinical hypothyroidism. Twenty-seven patients with subclinical hypothyroidism were compared with a control group of 20 age- and sex-matched subjects to determine whether subclinical hypothyroidism can lead to alterations in peripheral nerves or in the brainstem auditory evoked potentials (BAEPs). None of the patients had carpal tunnel syndrome or any other neurological or metabolic disturbances. Disease duration (expressed as the time from diagnosis of subclinical hypothyroidism to the time of neurological testing) ranged from less than 1 month to 6 months (median 2.5 months). We studied the distal motor latency, nerve conduction velocity (NCV), compound muscle action potentials, and F response in the median and peroneal nerves whereas the sensory nerve conduction velocity and sensory potential amplitude were measured in the sural and median nerves. Electrophysiological parameters and interpeak latencies yielded no significant difference between patient and control groups. The present study indicates that subclinical hypothyroidism of short duration does not lead to abnormalities of peripheral nerves or brainstem auditory evoked potentials.

[Hypothyroid hypertrophic myopathy in adults related to chronic lymphocytic thyroiditis. A case]

The authors report a case of hypothyroid hypertrophic myopathy which reveal chronic lymphocytic thyroiditis. This entity est uncommon, can be the most important sign of hypothyroidism and cure after the institution of thyroid hormone replacement therapy. The E. M. G. is usually myopathic and serum muscle markers (myoglobin and enzymes) increased. Pathologic studies of muscle show caracteritic but non specific and inconstant abnormalities. Hypothyroid myopathy could be caused by a mitochondrial oxidative phosphorylation deficiency or changes in muscle contractile properties (both in fibre type proportion and in the properties of the muscle contractile proteins).