Thyrotoxic Muscle Paralysis as a Rare Cause of Reversible Muscle Weakness: A Case Report

Thyrotoxic periodic paralysis is a clinical condition characterized by muscle weakness in patients with underlying hyperthyroidism. It is usually more commonly seen in patients of Asian origin and has a predisposition for the male population (unlike other thyroid disorders which commonly affect the female population). Findings are more overt in patients who have subclinical hyperthyroidism and there is a risk of them remaining untreated. The symptoms can range from mild muscle weakness to total paralysis. The muscles affected predominantly are the proximal and lower extremities group of muscles. Thyrotoxic muscle paralysis can be precipitated by hyperinsulinemic states such as after heavy meals, physical exertion, obesity, stress, and certain medications like high-dose steroids, antiretrovirals, and interferon therapy. The acute intervention usually revolves around the replenishment of patient's potassium stores followed by maintenance therapy with anti-thyroid medications. We present a case of a Chinese adolescent who presented to us with lower muscle weakness and underlying subclinical hyperthyroidism. It's important for clinicians to be familiar with this disease entity and include it in their differentials whenever a patient with muscle weakness presents. The treatment is simple and can result in rapid improvement of symptoms and should be initiated quickly.

A Literature Review on Thyrotoxic Periodic Paralysis

Thyrotoxic periodic paralysis (TPP) is a rare disease of the muscles that presents with painless weakness of the muscles. The patients usually have hypokalemia and hyperthyroidism with elevations in the level of triiodothyronine (T3) and thyroxine (T4). The muscle weakness is usually transient, and the patients in many cases suffer from recurrent episodes of muscle paralysis. This flaccid muscle paralysis predominantly affects the proximal and lower extremities group of muscles more than the distal and upper extremity muscles. This condition is one of the drastic complications of Graves's disease and, unfortunately, may require admission and treatment in the critical care units. It is often not recognized during the initial attack in the American population as the prevalence is very low among the Caucasian population and people from North America. However, while the prevalence is extremely low in the Caucasian population, it is known to be 10 times more common among the Asian population when compared with the Caucasian population. Furthermore, while the diseases of the thyroid gland are more common in females, this rare disease predominantly affects male sex. It is treated by reversing the hypokalemia, which can in itself prove to be fatal if not corrected quickly, and this is followed by treatment to restore the euthyroid state. A literature review on this reversible cause of muscle weakness is very important to better understand this disease.

Thyrotoxic Periodic Paralysis: An Incidental Diagnosis!

Thyrotoxic periodic paralysis is a rare presentation of thyrotoxicosis where the patient develops a transient motor deficit secondary to acute hypokalemia. The thyroid hormone augments gene transcription and post-transcriptional modification of Na-K ATPase, a cell membrane protein that regulates the electrical potential of the cell. Na-K ATPase increases active transport of potassium (K+) ions into the intracellular compartment causing hypokalemia without total body potassium deficit. Severe hypokalemia affects depolarization of the muscle cell membrane, clinically evidenced as paralysis. Other factors that may trigger hypokalemia and paralysis in the setting of hyperthyroidism include diet intake high in carbohydrates and salt, alcohol ingestion, trauma, infections, certain medication, and strenuous exercise. This rare but possible clinical presentation of thyrotoxicosis is significantly more predominant in males of Asian descent. We are reporting a case of a 44-year-old Asian-American male who presented to the emergency department with complaints of acute onset of bilateral lower extremity weakness. He had severe hypokalemia and was diagnosed with primary hyperthyroidism due to Graves' disease.

The prospective protective effect of selenium nanoparticles against chromium-induced oxidative and cellular damage in rat thyroid

Background

Nanotechnology has enabled researchers to synthesize nanosize particles that possess increased surface areas. Compared to conventional microparticles, it has resulted in increased interactions with biological targets.

Objective

The objective of this study was to determine the protective ability of selenium nanoparticles against hexavalent chromium-induced thyrotoxicity.

Design

Twenty male rats were used in the study, and arbitrarily assigned to four groups. Group 1 was the control group, and was given phosphate-buffered saline. Group 2 was the chromium-treated group and was given K₂Cr₂O₇ 60 μg/kg body weight intraperitoneally as a single dose on the third day of administration. Group 3 was the nano-selenium-treated group and was given selenium nanoparticles (size 3–20 nm) 0.5 mg/kg body weight intraperitoneally daily for 5 consecutive days. Group 4 was the nano-selenium chromium-treated group, which received selenium nanoparticles for 5 days and a single dose of K₂Cr₂O₇ on the third day of administration.

Materials and methods

Blood samples were collected from rats for measuring thyroid hormones (free triiodothyronine [T₃] and free thyroxine [T₄]) and oxidative and antioxidant parameters (malondialdehyde [MDA], reduced glutathione [GSH], catalase, and superoxide dismutase [SOD]). Upon dissection, thyroid glands were taken for histopathological examination by using paraffin preparations stained with hematoxylin and eosin (H&E) and Masson’s trichrome. Immunohistochemical staining was performed for detecting cellular proliferation using Ki67 antibodies.

Results

The present study shows that K₂Cr₂O₇ has a toxic effect on the thyroid gland as a result of inducing a marked oxidative damage and release of reactive oxygen species. This was shown by the significant decrease in free T₃ and T₄ and GSH levels, which was accompanied by significant increases in catalase, SOD, and MDA in the chromium-treated group compared to the control group. Se nanoparticles have a protective effect on K₂Cr₂O₇-induced thyroid damage, as a result of correcting the free T₃ and T₄ levels and GSH, catalase, SOD, and MDA compared to the K₂Cr₂O₇-treated group. Administration of nano-selenium alone in the nano-selenium-treated group had no toxic effect on rats’ thyroid compared to the control group. The biochemical results were confirmed by histopathological, immunohistochemical and pathomorphological studies.

Fatty acid metabolism and thyroid hormones

The importance of thyroid hormone signaling in the acute regulation of metabolic activity has been recognized for decades. Slowly, the underlying mechanisms responsible for this activity are being elucidated. A prominent characteristic of thyroid signaling is rapid increases in oxygen consumption and ATP production. This discovery implicated a non-genomic regulation of mitochondrial metabolism by thyroid hormones. Another important clue came from the discovery that thyroid hormones stimulated fatty acid oxidation (FAO) in a variety of tissues in a receptor-dependent, but transcriptional-independent manner. Recently, key linkages between thyroid hormone signaling and specific mitochondrial-targeted pathways have been discovered. This review focuses on the molecular mechanisms by which mitochondrial FAO can be increased through thyroid hormone signaling. The roles of both the full-length and shortened mitochondrial isoforms of thyroid hormone receptor will be discussed. Additionally, the impact of thyroid hormone signaling on dyslipidemias such as obesity, type II diabetes, and fatty liver disease will be considered.