Thyrotoxic Periodic Paralysis as a Presentation of Thyrotoxicosis: A Case Report

Abstract

Thyrotoxic periodic paralysis (TPP) is a rare but potentially serious complication of
hyperthyroidism characterized by muscular weakness and hypokalemia in a patient
with thyrotoxicosis. It is predominantly seen in Asian males.The etiology of
thyrotoxicosis in most of the cases of TPP is Graves’ disease. We present a case of a
19-year-old male who presented in emergency with paraparesis. Investigations
revealed hypokalemia and thyrotoxicosis related to toxic nodular goitre. Diagnosis of
thyrotoxic periodic paralysis was made and patient was treated with potassium
replacement, propranolol and antithyroid treatment.

Full text

Case Report
© ADR Journals 2016. All Rights Reserved.
Thyrotoxic Periodic Paralysis as a
Presentation of Thyrotoxicosis: A Case
Report
Abstract
Thyrotoxic periodic paralysis (TPP) is a rare but potentially serious complication of
hyperthyroidism characterized by muscular weakness and hypokalemia in a patient
with thyrotoxicosis. It is predominantly seen in Asian males.The etiology of
thyrotoxicosis in most of the cases of TPP is Graves’ disease. We present a case of a
19-year-old male who presented in emergency with paraparesis. Investigations
revealed hypokalemia and thyrotoxicosis related to toxic nodular goitre. Diagnosis of
thyrotoxic periodic paralysis was made and patient was treated with potassium
replacement, propranolol and antithyroid treatment.
Introduction
Periodic paralysis is a group of neuromuscular disorders of different etiologies
characterized by paroxysmal, short-lasting hypo-reflexic skeletal muscle weakness of
limbs without any sensory involvement and loss of consciousness. These disorders
can be classified into familial or primary periodic paralysis and secondary periodic
paralysis. Primary periodic paralysis is due to single-gene mutations leading to
abnormalities of sodium, potassium, calcium and chloride channels on membranes of
muscle cells. Hence, they are also called as channelopathies.1 Secondary periodic
paralysis may be due to known causes such as thyrotoxicosis, chronic renal failure,
paramyotonia congenita or may be associated with the use of drugs like ACE
inhibitors, angiotensin-II-receptor blockers or diuretics. The serum potassium levels
are usually altered during attacks in both primary and secondary periodic paralysis
which may be low, high or normal. In primary periodic paralysis the potassium levels
are normal in between the attacks, whereas it may remain abnormal in secondary
periodic paralysis in the inter-ictal period.2 Primary hpokalemic periodic paralysis has
been reported to be the commonest among all types of periodic paralysis. Thyrotoxic
periodic paralysis (TPP) is the most common cause of secondary or acquired periodic
paralysis.
Case Report
A 19-year-old male patient presented to the medical emergency with history of
sudden onset of weakness of both lower limbs. As per the patient’s history, he slept
at night normally but on waking up in the morning he was not able to stand or walk.
There was no history of preceding fever, vomiting, diarrhea, trauma or seizures. He
was a nonsmoker and nonalcoholic. On examination, patient was conscious and
oriented, his pulse rate was 104 beats/min and BP was 110/70 mmHg and rest of
general physical examination was unremarkable. Systemic examination revealed
power of 0/5 in all muscle groups in both the lower limbs and 3/5 in all muscle
groups in upper limbs. Examination of other systems was normal. Routine
investigations were normal except for the presence of severe hypokalemia with a
serum potassium of 1.6 meq/L (normal range 3.5–5.0 meq/L), serum phosphorus
level of 3.4 mg/dL (normal range 3–4.5 mg/dL) and mild hypomagnesemia with
serum magnesium level of 1.5 mg/dL (normal range 1.8–3.0 mg/dL). ECG showed
Naresh Kumar
1
, Sanjay
Pandit2, Pratap Singh3
1,2Associate Professor,
Department of Medicine,
Maulana Azad Medical
College, New Delhi-2.
3Associate Professor,
Department of Medicine,
Post Graduate Institute of
Medical Education and
Research and associated
Ram Manohar Lohia
Hospital, New Delhi.
Correspondence to:
Dr Naresh Kumar, Associate
Professor of Medicine,
16/554, Joshi Road Karol
Bagh, New Delhi-110005.
E-mail Id: drnareshmamc@
gmail.com
How to cite this article:
Kumar N, Pandit S, Singh P.
Thyrotoxic Periodic Paralysis
as a Presentation of
Thyrotoxicosis: A Case
Report. J Adv Res Med 2016;
3(2&3): 18-21.
ISSN: 2349-7181

J. Adv. Res. Med. 2016; 3(2&3) Kumar N et al.
19 ISSN: 2349-7181
hypokalemic changes with prolonged PR interval,
increased P-wave amplitude and widened QRS
complexes. He was managed with intravenous
potassium infusion followed by oral potassium
supplementation. He had complete recovery from
weakness within 12 hours of starting the therapy.
After recovery his history was reviewed in detail which
revealed symptoms of weight loss, increased appetite
and intermittent palpitations since last 4 months. There
was also a history of sudden death in family where his
elder brother died 2 years back and his mother was on
levothyroxine replacement therapy for primary
hypothyroidism since last 5 years. Detailed examination
revealed a multinodular goiter which was confirmed on
ultrasonography. Thyroid function tests revealed Free T4
of 55.3 pmol/L (normal range: 10–23 pmol/L), freeT3 of
11.6 pmol/L (normal range: 2–7 pmol/L) and a TSH level
of <0.15mIU/L (normal range: 0.5–4.7 mIU/L).
Radioactive iodine uptake scan showed a toxic nodule
(increased iodine uptake in the nodule). There was no
exophthalmos, sensory or cranial nerve deficits. He was
managed with oral potassium supplements and
propranolol. The patient showed dramatic improvement
of his symptoms. The patient was discharged on tablet
Carbimazole 10 mg three times a day, with the dose
being monitored based on FT4 level regularly. His final
diagnosis was thyrotoxic periodic paralysis secondary to
toxic nodular goiter. His thyroid function tests returned
to normal after 6 weeks of antithyroid therapy.
Potassium supplements and propranolol were stopped
after 2 weeks of discharge and antithyroid therapy was
continued. His potassium levels have been maintained
within normal limits since then and there has been no
further episode of weakness.
Discussion
TPP is a rare syndrome characterized by muscular
weakness and paralysis associated with hypokalemia in
a predisposed patient with thyrotoxicosis.3 TPP can
occur in any ethnicity but majority of cases are seen in
Asian males, in the age group of 20–40 years.4,5
Although hyperthyroidism is more common in females,
TPP is seen more commonly in males with a male-to-
female ratio of 20:1 or higher.6 The incidence of TPP is
approximately 2% in patients with thyrotoxicosis of any
cause.7 In an Indian study on 30 cases of hypokalemic
periodic paralysis, thyrotoxicosis was found in 16.7% of
all cases.8 Although TPP is most commonly seen in
Graves’ disease, it can occur with thyrotoxicosis of any
cause and it is not related to severity or duration of
thyrotoxicosis.7 The etiology of thyrotoxicosis in our
case was toxic nodular goitre.
Precipitating factors of TPP include high carbohydrate
diet, rest after strenuous exercise, cold exposure,
infection, alcohol and emotional stress. Weakness in
majority of cases develop at night or early morning.4
There is also a seasonal predilection for patients of TPP
to develop the crisis in warmer months.4,7 TPP most
commonly presents in third to fourth decade of life as
rapid onset, transient, symmetrical muscular weakness
associated with hypokalemia. The lower limbs are
predominantly affected but it can involve all four limbs.
Proximal muscle groups are more severely affected than
the distal muscle groups in the limbs.9,10 The paralysis is
reversible with correction of hypokalemic and
hyperthyroid state; however, the condition is potentially
life-threatening as severe hypokalemia can result into
arrhythmia and respiratory failure may ensue due to
bulbar and diaphragmatic weakness.
The pathogenesis of periodic paralysis in TPP is not clear
yet. Transcellular distribution of potassium is
maintained by the Na+/K+− ATPase activity in the cell
membrane, and it is mainly influenced by the action of
insulin and beta-adrenergic catecholamines.11
Hypokalemia in TPP is thought to result from an
intracellular shift of potassium and not total body
depletion. It has been shown that the Na+/K+ ATPase
activity in platelets and muscles is significantly higher in
patients with TPP.12 Hyperthyroidism results in a hyper-
adrenergic state, which may lead to the activation of the
Na+/K+ ATPase pump which results in increased cellular
uptake of potassium.5,11 Thyroid hormones especially T3
may also directly stimulate Na+/K+ ATPase activity and
increase the number and sensitivity of beta
receptors.11,13 Cases of TPP associated with normal K
level have also been seen, which indicates the role of
some factors other than hypokalemia. Treatment of
these patients with beta blockers and antithyroid drugs
without potassium replacement prevents further
attacks in TPP indicating the involvement of thyroid
hormones in the pathogenesis of TPP.10,14,15 Patients
with TPP have also been found to have hyperinsulinemia
during episodes of paralysis and increased basal insulin
levels in between the attacks, which may be secondary
to the hyper-adrenergic state related to
hyperthyroidism.16 This may explain the attacks
occurring after high-carbohydrate meals. However,
weakness in TPP cannot be fully explained by these
mechanisms as TPP occurs only in minority of patients
with hyperthyroidism. Thus, additional factors, like
genetic predisposition are presumed to contribute and
may also explain the racial difference in prevalence of
this condition. Few genetic mutations in the K channel
gene (KCNE3) and several gene polymorphisms have
been reported in literature.3 A new gene KCNJ18 has

Kumar N et al. J. Adv. Res. Med. 2016; 3(2&3)
ISSN: 2349-7181 20
been identified which is located on 17p11.1-2 encodes
an inwardly rectifying potassium channel (Kir2.6). Kir2.6
mutations have been found in 33% of patients with TPP
and are thought to be leading to hypokalemia by
interfering with assembly of K channel.17 The diurnal
variation in potassium movement where there is
nocturnal potassium influx into skeletal muscle would
explain the tendency for thyrotoxic periodic paralysis to
occur at night.18
Hypokalemia is the most common electrolyte
abnormality seen during an acute crisis. Besides
hypokalemia, hypophosphatemia and hypomagnesemia
are also known to occur in association with thyrotoxic
periodic paralysis. The correction of hypophosphatemia
without phosphate administration supports the
possibility of intracellular shift of phosphate. The most
common arrhythmias in TPP are sinus tachycardia, atrial
flutter, atrial fibrillation, extrasystoles and paroxysmal
supraventricular tachycardia. Electrocardiographic
findings are supportive of a diagnosis of TPP rather than
sporadic or familial periodic paralysis are sinus
tachycardia, elevated QRS voltage and first-degree AV
block (sensitivity 97%, specificity 65%). In addition to ST-
segment depression, T-wave flattening or inversion and
the presence of U waves are typical of hypokalemia.19
The management of TPP includes treatment of acute
attack as well as treatment of the underlying condition
to prevent future attacks. The paralytic symptoms and
signs improve as potassium returns from intracellular
space back into the extracellular space.6 Rapid
administration of oral or intravenous potassium chloride
can abort an attack and prevent cardiovascular and
respiratory complications.5 A lower dose of potassium is
the treatment of choice for facilitating recovery and
reducing rebound hyperkalemia due to release of
potassium and phosphate from the cells on recovery.3
Rebound hyperkalemia occurred in approximately 40%
of patients with TPP, especially if they received >90
mmol of potassium chloride within the first 24 hours.
Additionally, propranolol, a nonselective blocker, which
prevents the intracellular shift of potassium and
phosphate by blunting the hyperadrenergic stimulation
of Na+/K+ ATPase, should be given as an adjunct for the
remission of the acute crisis and prevention of
recurrences till euthyroid state is established.20 The
definitive therapy forTPP includes treatment of
hyperthyroidism with antithyroid medications, surgical
thyroidectomy, or radioiodine therapy.21
TPP is a serious complication of thyrotoxicosis. It is the
commonest secondary cause of hypokalemic periodic
paralysis. This diagnosis must be considered in all cases
presenting with hypokalemic periodic paralysis as it
responds well to treatment and early diagnosis can
prevent potentially lethal complications of
thyrotoxicosis.
Conflict of Interest: None
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Date of Submission: 10th Oct. 2016
Date of Acceptance: 10th Oct. 2016