Hypothyroid myopathy. A clinical and pathological study

Abstract

Ten patients with varying degrees of hypothroid myopathy were studied clinically and by serial percutaneous needle muscle biopsies before and during treatment with L-thyroxine. The biochemical evidence of hypothyroidism was related to the severity of the myopathic and signs before treatment. The severity of myopathic symptoms before and during treatment correlated with the biochemical evidence of hypothyrodism, a type II fibre atrophy and increased central nuclear counts. Likewise, the clinical evidence of a myopathy before and during treatment was correlated with both a type II fibre atrophy and loss and increased central nuclear counts but was not related to the biochemical parameters of hypothyroidism, except the level of thyroid stimulating hormone. In the muscle, before and during treatment, of the two most severely affected patients, intracellular glycogen inclusions were seen in scattered muscle fibres. On light microscopy and on electronmicroscopy, numerous mitochondria were seen responding to L-thyroxine with accumulations of subsarcolemmal honey-combing. Vesicular abnormalities, an electron dense matrix or occasional crystalline deposits were seen in muscle mitochondria from less severely azffected patients. Severely myopathic muscle contained excessive glycogen, membrane bound glycogen and excess lipid in a mainly perinuclear distribution. Occasional myelin and membranous bodies were seen and satellite cells during the recovery phase. A group of patients with hypothyroid myopathy who are likely to have a delayed recovery of full muscle strength on L-thyroxine may be recognised by the presence of severe proximal muscle weakness and characteristic changes on histochemical and electronmicroscopic examination of muscle. The spectrum of histochemical and electronmicroscopic abnormalities of muscle revealed with increasing degree of hypothyrodism, suggests that a generally reversible acquired glycogen storage and mictochondrial disorder is an important feature in the pathogenesis of this condition.

Changes in myosin light chains in the rat soleus after thyroidectomy

“…The mechanism of this slowing in muscle contractile properties is uncertain but histochemical studies suggest that it may be related to changes in muscle fibre types. Selective atrophy and loss of type 2 (fasttwitch) fibres has been found in patients with longstanding hypothyroidism [6]. In the rat soleus, thyroidectomy leads to an increase in the proportion of type 1 (slow-twitch) fibres, consistent with the increase observed in alkali-lability of the myosin ATPase extracted from the muscle [7].…”

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

“…The severity of the myopathic picture seems to be related to some findings of muscular biopsy. In severe cases there is atrophy of type II muscular fibers, associated to central core of the nucleus, mainly of the type II muscular fiber 3 . On optic microscopy the alterations are atrophy, necrosis, muscular fibers hypertrophy, increase in the number of nucleus, ring-shaped fibers, glycogen deposits and increase of connective tissue 9 .…”

“…Myokymia may be another peripheral manifestation and it seems to be related to sodium loss 9 . There are different clinical presentations of the myopathy: weakness with muscular pseudohypertrophy, muscular atrophy or myasthenic syndrome 3 .…”

“…An impairment of peripheral nervous system and muscles leads to different types of neuropathy and myopathy being responsible for 5% of acquired myopathies 2 . The myopathy associated with hypothyroidism could be divided in four subtypes: KocherDebré-Semelaigne syndrome, Hoffman's syndrome, atrophic form and myasthenic syndrome 3 . In the Kocher-Debré-Semelaigne syndrome described in infants with cretinism, as in the Hoffman syndrome, patients presented with hypertrophy, muscular we-akness, slowness of mental and locomotor activities.…”

Hoffmann's Syndrome associated with Autoimmune Hypothyroidism: a Case Report

“…The most affected muscles are gastrocnemius, deltoid and trapezius [1][2][3]. Especially, presence of hypothyroidism can give rise to occur several symptoms in clinic such as fatigue, weight gain, cold intolerance, impaired memory, hoarseness, dry skin, muscle aches, tenderness, heart enlargement and myxedema coma [4].…”