Myopathies associated with hypothyroidism: a review based upon 13 cases

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.

Acute arthritis revealing Hashimoto's thyroiditis

Rheumatic manifestations can reveal hypothyroidism, such as arthritis and nonspecific musculoskeletal symptoms. We report herein the case of an acute polyarthritis revealing Hashimoto's thyroiditis (HT). Hormone replacement therapy leads to the resolution of arthritis related to HT, suggesting the role of thyroid hormone in the pathogenesis of arthritis.

Maternal hypothyroidism prolongs gestation period and impairs glucose tolerance in offspring of Wistar rats

OBJECTIVES

Pregnancy is a critical period keenly regulated by both maternal and foetal factors and a shift in these factors could result in severe complications manifesting in foetal and adult life. However, maternal hypothyroidism before and/or during pregnancy is a critical factor. This study investigated the effect of maternal hypothyroidism on glucose tolerance and thyroid function in male and female offspring.

METHODS

Fifteen adult female Wistar rats were divided into three groups: Group 1 (sham-control), Group 2 (thyrodectomized) and Group 3 (thyroidectomised + L-thyroxine treated). Blood thyroxine (T4) level was measured on the day 10 after thyroidectomy in Groups 1 and 2, and day 35 in Group 3. Males were introduced to the female rats after T4 measurement. At PND-112, T4 levels of their offspring were measured. Oral Glucose Tolerance Test (OGTT) was measured in offspring at PND-133.

RESULTS

Thyroxine reduced significantly in Group 2 and their offspring (male and female) compared to Group 3 while gestation period was prolonged significantly in Group 2 compared to Group 1. Hypothyroid male offspring showed depressed glucose tolerance, however, no effect was observed in female offspring.

CONCLUSIONS

This study suggests that maternal hypothyroidism prolonged gestation period, induced foetal hypothyroidism in both genders and depressed glucose tolerance in male offspring.

A Complex Case of Polymyositis Overlapping With Hypothyroid Myopathy Without Underlying Autoimmune Thyroid Disorder

A 78-year-old woman with a past medical history of hypothyroidism and Sjogren's syndrome presented with a two-month history of gradually progressive bilateral lower extremity weakness. Significant elevation in thyroid-stimulating hormone (TSH) and muscle enzyme, such as creatine kinase, was noticed on presentation. Due to concerns of hypothyroid myopathy, the patient was started on thyroxine and triiodothyronine supplementation. The patient reported no significant improvement in her weakness in the one-month follow-up. Laboratory workup revealed improving TSH levels but worsening creatine kinase levels. Electromyography study showed primarily myopathic features, such as abnormal insertional activity concerning for mild inflammatory myopathy. Muscle biopsy showed mild inflammatory exudate and features of myopathy with ongoing denervation. The patient was diagnosed with polymyositis and started on prednisone 0.5 mg/kg daily with a taper course and methotrexate. The patient reported significant improvement in her weakness when seen in six weeks with normalizing creatine kinase levels. The hallmark difference between hypothyroid myopathy (including polymyositis-like syndrome) and conventional polymyositis is the complete clinical recovery and resolution of laboratory abnormalities after treatment with thyroid hormone replacement in hypothyroid myopathy. There was no evidence of underlying autoimmune thyroid disorder which makes this case unique. This case highlights the complex case of polymyositis overlapping with hypothyroid myopathy with no underlying autoimmune disorder.

Early Developmental Disruption of Type 2 Deiodinase Pathway in Mouse Skeletal Muscle Does Not Impair Muscle Function

BACKGROUND

Myogenesis is positively regulated by thyroid hormone (triiodothyronine [T3]), which is amplified by the type 2 deiodinase (D2) activation of thyroxine to T3. Global inactivation of the Dio2 gene impairs skeletal muscle (SKM) differentiation and regeneration in response to muscle injury. Given that newborn and adult mice with late developmental SKM Dio2 disruption do not develop a significant phenotype, it was hypothesized that D2 plays an early role in this process.

METHODS

This was tested in mice with SKM disruption of Dio2 driven by two early developmental promoters: MYF5 and MYOD.

RESULTS

MYF5 myoblasts in culture differentiate normally into myotubes, despite loss of almost all D2 activity. Dio2 mRNA levels in developing SKM obtained from MYF5-D2KO embryos (E18.5) were about 54% of control littermates, but the expression of the T3-responsive genes Myh1 and 7 and Atp2a1 and 2 were not affected. In MYF5-D2KO and MYOD-D2KO neonatal hind-limb muscle, the expression of Myh1 and 7 and Atp2a2 remained unaffected, despite 60-70% loss in D2 activity and/or mRNA. Only in MYOD-D2KO neonatal muscle was there a 40% reduction in Atp2a1 mRNA. Postnatal growth of both mouse models and SKM function as assessed by exercise capacity and measurement of muscle strength were normal. Furthermore, an analysis of the adult soleus revealed no changes in the expression of T3-responsive genes, except for an about 18% increase in MYOD-D2KO SOL Myh7 mRNA.

CONCLUSION

Two mouse models of early developmental disruption of Dio2 in myocyte precursor exhibit no significant SKM phenotype.

Approach to asymptomatic creatine kinase elevation

How to manage a patient who has an elevated serum creatine kinase (CK) level but no or insignificant muscle-related signs and symptoms is a clinical conundrum. The authors provide a systematic approach, including repeat testing after a period of rest, defining higher thresholds over which pursuing a diagnosis is worthwhile, and evaluating for a variety of nonneuromuscular causes. They also outline a workup for neuromuscular causes.

Exercise responses in patients with chronically high creatine kinase levels

INTRODUCTION

Elevated serum creatine kinase (CK) is often taken to reflect muscle disease, but many individuals have elevated CK without a specific diagnosis. How elevated CK reflects muscle metabolism during exercise is not known.

METHODS

Participants (46 men, 48 women) underwent incremental exercise testing to assess aerobic performance, cardiovascular response, and ventilatory response. Serum lactate, ammonia, and CK were measured at rest, 4 minutes into exercise, and 2 minutes into recovery.

RESULTS

High-CK and control subjects demonstrated similar aerobic capacities and cardiovascular responses to incremental exercise. Those with CK ≥ 300 U/L exhibited significantly higher lactate and ammonia levels after maximal exercise, together with increased ventilatory responses, whereas those with CK ≥200 U/L but ≤ 300 U/L did not.

CONCLUSIONS

We recommend measurement of lactate and ammonia profiles during a maximal incremental exercise protocol to help identify patients who warrant muscle biopsy to rule out myopathy. Muscle Nerve 56: 264-270, 2017.

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.

Rheumatic manifestations of endocrine disease

PURPOSE OF REVIEW

Musculoskeletal complaints are a feature of several endocrine diseases. This review will update clinicians on their association, presentation, and treatment.

RECENT FINDINGS

To update clinicians on the recent literature as it is related to pathophysiology, genetic, and clinical findings on the association of these diseases and musculoskeletal complaints.

SUMMARY

Rheumatologists in the clinic are faced with different presentations of various musculoskeletal complaints every day. Every new patient encounter requires the differential diagnosis of these complaints. The first task is usually to decide with what disease in internal medicine these complaints are associated. The endocrinopathies are a group of illnesses that either present initially or exhibit sometime during the course of the disease as a variety of musculoskeletal complaints. Rheumatic manifestations may often be the initial presentation of an endocrine disorder. Each endocrine disorder may also have its own arthritic complaints, which can present as a definitive rheumatic disease such as calcium pyrophosphate dihydrate deposition disease or as a rheumatic symptom such as diffuse arthralgia. The rheumatologist as well as the primary care physician should be knowledgeable about the ways in which muscles, tendons, ligaments, and joints are affected by diseases of the endocrine system.

Chronic myopathy due to immunoglobulin light chain amyloidosis

Amyloid myopathy associated with a plasma cell dyscrasia is a rare cause of muscle hypertrophy. It can be a challenging diagnosis, since pathological findings are often elusive. In addition, the mechanism by which immunoglobulin light-chain deposition stimulates muscle overgrowth remains poorly understood. We present a 53-year old female with a 10-year history of progressive generalized muscle overgrowth. Congo-red staining and immunohistochemistry revealed perivascular lambda light chain amyloid deposits, apparent only in a second muscle biopsy. The numbers of central nuclei and satellite cells were increased, suggesting enhanced muscle progenitor cell formation. Despite the chronicity of the light chain disease, the patient showed complete resolution of hematologic findings and significant improvement of her muscle symptoms following autologous bone marrow transplantation. This case highlights the importance of early diagnosis and therapy for this treatable cause of a chronic myopathy with muscle hypertrophy.

Hoffmann's syndrome and pituitary hyperplasia in an adolescent secondary to Hashimoto thyroiditis

BACKGROUND

Diffuse muscle hypertrophy is a rare complication of acquired hypothyroidism. When accompanied by stiffness, weakness, and painful muscle cramps, the condition is known as Hoffmann's syndrome (HS). HS is usually seen in young adults due to long-standing untreated primary hypothyroidism. We report a very rare case of HS with muscle hypertrophy and pituitary hyperplasia complicating hypothyroidism in an adolescent.

CASE

A 12-year-old male admitted with muscle pain, headache, and fatigue. He had marked hypertrophy of both calf and shoulder muscles. Laboratory tests indicated elevated muscle enzymes and lipids with an elevated thyrotropin and low thyroxine levels. Hashimoto thyroiditis was confirmed on thyroid studies. He had also papilledema bilaterally and magnetic resonance imaging showed an enlargement of the pituitary gland. Treatment with thyroid hormone resulted in complete improvement of symptoms within 3 months.

CONCLUSIONS

HS is a rare but treatable form of acquired myopathies and can be seen in children due to untreated hypothyroidism. All patients with an acquired myopathy and muscular pseudohypertrophy should be screened regarding thyroid hormones.

Electrodiagnostic approach to the patient with suspected myopathy

Electrodiagnostic testing is a useful component of the approach to a patient with suspected myopathy. It follows the history and is guided by the neurologic examination findings. Uncovering various electrodiagnostic patterns (eg, fibrillation potentials with short-duration motor unit potentials, short-duration motor unit potentials without fibrillation potentials, myotonic discharges, and short-duration motor unit potentials with complex repetitive discharges) can lead to more targeted laboratory testing and a refined differential diagnosis. Electromyography may also be used to detect subclinical myopathy, assess disease activity, and help select a suitable muscle for biopsy.

Fall prevention and vitamin D in the elderly: an overview of the key role of the non-bone effects

Preventing falls and fall-related fractures in the elderly is an objective yet to be reached. There is increasing evidence that a supplementation of vitamin D and/or of calcium may reduce the fall and fracture rates. A vitamin D-calcium supplement appears to have a high potential due to its simple application and its low cost. However, published studies have shown conflicting results as some studies failed to show any effect, while others reported a significant decrease of falls and fractures. Through a 15-year literature overview, and after a brief reminder on mechanism of falls in older adults, we reported evidences for a vitamin D action on postural adaptations - i.e., muscles and central nervous system - which may explain the decreased fall and bone fracture rates and we underlined the reasons for differences and controversies between published data. Vitamin D supplementation should thus be integrated into primary and secondary fall prevention strategies in older adults.

Rheumatic manifestations of endocrine diseases

PURPOSE OF REVIEW

Musculoskeletal complaints accompanying or as a result of endocrine disorders are common and have been well described. This review re-examines these associations in light of newer information on biology and genetics.

RECENT FINDINGS

In this article, we describe the recent studies on pathophysiology of the muscular skeletal complaints in endocrine disease. In addition we report on population as well as genetic studies, which address the relationship between endocrine and rheumatologic disease, both of which are autoimmune.

SUMMARY

Very often, the presentation of rheumatic manifestations is the initial presentation of endocrine disease. Being aware of the presentation as well as the unique physiology of these complaints will help alert the clinician to an early diagnosis of endocrine disease. In addition understanding whether certain endocrine disease occurs more often in rheumatologic illness will enable the clinician to investigate their occurrence early, leading to earlier intervention and resulting in decreased morbidity from these concomitant illnesses.

Onset of hypothyroidism with polymyositis-like clinical features in elderly patients

Impaired muscle function may be a predominant aspect of hypothyroidism and is virtually present in all patients with overt thyroid failure. Less common is the onset of hypothyroidism with clinical features mimicking a polymyositis. We have observed 3 patients, whose age ranged 63-68 years, presenting with muscle aches, cramps, proximal weakness and stiffness. Two patients had dysphagia. Serum creatine kinase (CK) and electromyography (EMC) were altered in two patients. Muscle biopsy showed type II atrophy, sporadic type I and type II grouping, "core-like" areas, and some myopathic changes such as central nuclei and muscle necrosis. No inflammatory changes were present. Immunohistochemistry of several muscle cytoskeletal proteins revealed increased desmin in "corelike" areas. Detection of serum thyroid hormone levels revealed very low triiodo-L-thyronine (T3) and thyroxine (T4), whereas thyroid-stimulating hormone (TSH) was greatly increased as well as serum anti-thyroglobulin, anti-peroxidase and anti-microsome antibodies. The patients were diagnosed having a hypothyroid myopathy due to Hashimoto thyroiditis. L-thyroxine treatment normalized clinical and hormone levels, but serum antibodies remained elevated. Muscle biopsy was fundamental to establish the correct diagnosis in our patients. Presence of over-expression of desmin in cores, as described in target lesions in neurogenic diseases, may suggest a nerve-mediated pathogenesis of hypothyroid myopathy.

Relationship between age and serum thyrotropin among asymptomatic older people in Taiwan

Hypothyroidism is a common disorder in older people, and may be asymptomatic and hard to be diagnosed. The main purpose of this study was to evaluate the distribution of serum thyrotropin (thyroxin-stimulating hormone, TSH) among asymptomatic older people in Taiwan, and to evaluate the relationship between age and serum TSH. In 2007, all subjects participating in the annual elderly health examinations at Taipei Veterans General Hospital were invited for study and were enrolled when they were fully consented. In total, 1716 asymptomatic elderly people (mean age: 73.2+/-4.4 years, 56.3% males) participated in this study after careful exclusion of 38 subjects with past history of thyroid disorders. All participants were divided into two groups: (1) younger old (age 65-79) and (2) older old (age over 80) for further analysis. The mean serum levels of TSH were similar between younger old and older old groups (2.43+/-5.36 microIU/ml for younger old and 2.36+/-3.51 microIU/ml for older old, p=0.444). The overall prevalence of suspected hypothyroidism was 9.2% among asymptomatic older people in Taiwan, which was significantly lower than in Caucasians. The prevalence of suspected hypothyroidism may reach 25.9% if the TSH cutoff was lowered to 2.5 microIU/ml. Further study is needed to determine the normal reference range of serum TSH in older people.

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.

Electrodiagnostic approach to the patient with suspected myopathy

Uncovering the cause of a suspected myopathy may be challenging. However, a careful approach starts with utilizing the wealth of available information regarding the clinical and laboratory features of myopathy. Electrodiagnostic testing is then obtained (in most cases). Recognition of the pattern of EMG findings in light of the clinical and laboratory features should narrow the differential diagnosis and dictate the next steps in the evaluation. Histopathologic or molecular studies, or both may follow. Ultimately, this approach usually allows the clinician to make the correct diagnosis.

Polymyositis-like syndrome in hypothyroidism: review of cases reported over the past twenty-five years

Polymyositis-like syndrome, with proximal muscle weakness and elevation of muscle enzymes, may be a clinical manifestation of hypothyroidism. To define the clinical, biochemical, electromyographic, and pathologic characteristics of patients with this syndrome, we identified and reviewed by MEDLINE all cases reported in the English literature from January 1, 1975 through December 31, 2000. Thirty-two cases were considered. Fifty-nine percent of the patients were male with a mean age of 54.7 +/- 22.6 years, (+/- 1 standard deviation [SD]). Weakness was described in 100% of patients. Other common clinical manifestations were: delayed tendon reflexes with slow relaxation phase (41%), muscle tenderness (25%), and muscle induration (9%). The mean creatine kinase (CK) was 2164 +/- 1954 U/L (+/- 1 SD) and the mean thyroid-stimulating hormone (TSH) was 114.8 +/- 85.6 mIU/L (+/- 1 SD). Fifty percent of patients had electromyography; half of the studies were normal while the other half showed nonspecific myopathic changes. Biopsies were performed in 80% of the patients. The most common findings were type II fiber atrophy, type I fiber hypertrophy, central nuclei disposition, necrosis, increased percentage of type I fibers, and decreased percentage of type II fibers, inflammatory infiltrate and the presence of core-like structures. The characteristics of polymyositis-like syndrome in hypothyroidism did not differ from those of nonspecific hypothyroid myopathy. Clinical judgment alone may not be sufficient to suspect and detect these patients. Serum TSH levels should be routinely determined in all patients with muscle weakness or elevation of creatine kinase.

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.

Myopathy as the persistently isolated symptomatology of primary autoimmune hypothyroidism

Although disorders of thyroid function may cause a wide range of muscle disturbances, an overt myopathy has been rarely reported as an isolated clinical presentation of hypothyroidism. We observed 10 patients (5 males and 5 females) who had been referred to the department of neurology because of muscular fatigability, myalgia, cramps, or proximal weakness. Laboratory investigation showed that all patients had hypothyroidism due to Hashimoto's thyroiditis (atrophic variant in 9/10). Classic symptoms/signs of hypothyroidism such as lethargy, constipation, cold intolerance, myxedematous facies, and/or bradycardia were absent, as assessed independently by the three coauthoring thyroidologists. Muscular complaints improved greatly and then disappeared after substitutive levothyroxine treatment. Muscle biopsy revealed nonspecific changes. Nicotinamide adenine dinucleotide reductase (NADH-TR)-hyporeactive cores were present in two patients (10% and 90% of type 1 fibers). On electron microscopy, the core areas showed disorganized myofibrils, Z-band streaming, rod formation, and paucity of mitochondria and glycogen granules. Desmin intermediate filaments were overexpressed only in some cores. The similarity of the pattern of desmin expression between hypothyroid cores and target lesions of denervated fibers supports the hypothesis that, at least in some of our patients, myopathy was the result of an impaired nerve-mediated action of thyroid hormones on skeletal muscle. Our observations suggest that an isolated myopathy as the sole manifestation of hypothyroidism is not a rare event. We postulate that our cases may constitute a peculiar subgroup of Hashimoto's thyroiditis patients: (1) the strikingly abnormal F/M ratio of 1:1; (2) the relatively younger age; (3) the rarity of the goitrous variant; (4) the unusual finding of antithyroglobulin (Tg-Ab) > antithyroid peroxidase (TPO-Ab). Thorough evaluation of thyroid function is appropriate in patients with myopathy of uncertain origin.

Serum creatine kinase levels in overt and subclinical hypothyroidism

Overt hypothyroidism is known to be associated with increased serum creatine kinase (CK) levels. However, there is little information on CK levels in subclinical hypothyroidism. The aim of the study was to assess the relationship between CK levels and thyroid function in overt and subclinical hypothyroidism. Thyroid function tests (thyrotropin [TSH], free thyroxine [FT4], free triiodothyronine [FT3]) and the serum levels of CK were obtained from 23 patients admitted to a general hospital for illnesses other than thyroid or muscular diseases, myocardial ischemia, or brain damage. Overt hypothyroidism, based on thyroid function tests, was present in 10 patients, whereas hypothyroidism could be classified as subclinical in the other 13. A positive correlation was observed between CK and thyrotropin, and to a lesser extent between CK and thyroid hormones. Moreover, the correlation between CK and TSH and between CK and FT4 was detectable in subclinical hypothyroidism. Our data suggest that even in subclinical hypothyroidism there is some degree of dysfunction in skeletal muscle metabolism.

Neurological manifestations of hypothyroidism: a retrospective study of 29 dogs

Neuromuscular signs in association with hypothyroidism are described in 29 dogs. Eleven dogs had lower motor neuron signs, 9 had peripheral vestibular deficits, 4 had megaesophagus, and 5 had laryngeal paralysis. Primarily older (mean = 9.5 years), large-breed dogs were affected, and there was no sex or breed predisposition. Duration of clinical signs before presentation ranged from 2 to 8 weeks (mean = 5 weeks). The diagnosis was based on (1) results of neurological examination (29 dogs); (2) electromyographic abnormalities (18 dogs), including fibrillation potentials (n = 18), positive sharp waves (n = 15), and complex repetitive discharges (n = 4); (3) high serum cholesterol concentration (10 dogs; mean = 335 mg/dL); (4) low response to thyroid-stimulating hormone (29 dogs; mean T4 prestimulation concentration = 0.8 micrograms/dL; mean T4 poststimulation = 1.2 microgram/dL); and (5) good response to thyroxine supplementation (26 dogs). Dogs with vestibular deficits had abnormal brainstem auditory-evoked responses (BAER), including increased latencies of P1-P6 and decreased amplitude of P4,5-N5. Seven other dogs had similar BAER abnormalities without manifesting clinical signs of vestibular involvement. Three dogs with vestibular signs had fibrillation potentials and positive sharp waves without exhibiting lower motor neuron signs. All dogs were supplemented with levothyroxine (0.02 mg/kg PO bid). The follow-up period ranged between 6 and 30 months (mean, 14 months). Serum T4 concentrations were measured at least 3 times for each dog every 2 months (mean T4 concentration = 2.6 micrograms/dL). All but 1 dog with lower motor neuron signs and 1 dog with vestibular signs recovered after 2 months (mean, 57 days).(ABSTRACT TRUNCATED AT 250 WORDS)

[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).