Thyroid Research and Practice

CASE REPORT
Year
: 2014  |  Volume : 11  |  Issue : 2  |  Page : 73--75

Ocular myasthenia with thyroid associated ophthalmopathy in subclinical Graves' disease: Diagnostic challenge and treatment outcomes


Krishna Biswas1, Meha Sharma2, Deep Dutta3, Navjyoti Barman1,  
1 Department of Endocrinology, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi, India
2 Department of Medicine, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi, India
3 Department of Endocrinology and Metabolism, Institute of Post Graduate Medical Education and Research and Seth Sukhlal Karnani Memorial Hospital, Calcutta, West Bengal, India

Correspondence Address:
Deep Dutta
Room-9A, 4th Floor Ronald Ross Building, Department of Endocrinology and Metabolism, Institute of Post Graduate Medical Education and Research and Seth Sukhlal Karnani Memorial Hospital, 244 AJC Bose Road, Kolkata - 700 020, West Bengal
India

Abstract

Ocular myasthenia in Graves«SQ» disease is very rare with less than 10 cases reported. We present a clinically euthyroid lady with features of thyroid-associated ophthalmopathy (TAO) who had mild ptosis, external ophthalmoplegia, firm goiter and subclinical hyperthyroidism. Hertel exophthalmometry confirmed exophthalmos. CT orbit revealed thickening of bilateral inferior, medial and superior recti. Anti-thyroid peroxidase antibody was positive (154 IU/ml; normal <40 IU/ml). Repetitive nerve stimulation test of bilateral nasalis muscle showed decremental response, more prominent on the left side. Electrodiagnostic screening for concomitant myopathy or neuropathy was unremarkable. A subsequent positive neostigmine test and a positive anti-acetylcholine receptor antibody (1.46 nmol/L; normal <0.5 nmol/L) lead to the diagnosis of ocular myasthenia with TAO and subclinical Graves«SQ» disease. Ptosis and ophthalmoplegia improved with pyridostigmine and carbimazole. She was doing well even after 2 years of follow-up. Any patient of TAO with ptosis and ophthalmoplegia should be evaluated for ocular myasthenia. This case intends to highlight that TAO and ocular myasthenia can coexist, is a diagnostic challenge, with important consequences, as lack of treatment of Graves«SQ» disease can aggravate myasthenia.



How to cite this article:
Biswas K, Sharma M, Dutta D, Barman N. Ocular myasthenia with thyroid associated ophthalmopathy in subclinical Graves' disease: Diagnostic challenge and treatment outcomes.Thyroid Res Pract 2014;11:73-75


How to cite this URL:
Biswas K, Sharma M, Dutta D, Barman N. Ocular myasthenia with thyroid associated ophthalmopathy in subclinical Graves' disease: Diagnostic challenge and treatment outcomes. Thyroid Res Pract [serial online] 2014 [cited 2022 Jan 26 ];11:73-75
Available from: https://www.thetrp.net/text.asp?2014/11/2/73/129734


Full Text

 Introduction



Hyperthyroidism occurs in 3-8% of patients with myasthenia. [1] However, occurrence of ocular myasthenia in a patient with Graves' disease is uncommon with 10 cases being reported till date [2],[3],[4],[5],[6],[7] of which four patients had clinically silent Graves' disease. [3],[4],[5],[6] Clinically silent Graves' ophthalmopathy with ocular myasthenia is a diagnostic challenge due to significant overlap of the ocular manifestations. We present a 65-year-old lady with clinically silent Graves' disease, thyroid-associated ophtlamopathy (TAO), and ocular myasthenia.

 Case Report



A 65-year-old lady presented with eye pain, grittiness, redness and watering of a year duration (left > right). Examination was significant for bilateral proptosis (left > right), bilateral complete external ophthalmoplegia, mild ptosis (prominent in the left eye), zero clinical activity score, normal pupillary response, normal ophthalmoscopy, normal intraocular pressure, grade-Ib firm non-tender diffuse goiter and lack of features of thyrotoxicosis [Figure 1]. Hertel exophthalmometer gave readings of 21 and 20 mm in left and right eye respectively (normal <20 mm) with distance on the scale measuring 101 mm. She did not have bulbar and neck muscles involvement. Power in all four limbs were normal. She was a chronic smoker [1-2 packs of "bidi" (thin indigenous Indian cigarette made of tobacco flakes wrapped in tendu leaves)] since 20 years age.{Figure 1}

Investigations were significant for low TSH 0.05 mU/L (0.4-4.5 mU/L), normal T 3 154 ng/dl (60-181 ng/dl) and a normal T 4 12.2 μg/dl (8.2-12.8μg/dl). Anti-TPO antibody was 154 IU/ml (normal <37 IU/ml). Her 2-hour and 24-hour I 131 uptake was 6.8% and 30.6%, respectively, and thyroid scan was suggestive of diffuse radiotracer uptake in bilateral lobes. Fine needle aspiration cytology (FNAC) of thyroid showed numerous follicles with decreased colloid, infiltration of lymphocytes and fire-flare appearance. Contrast-enhanced computerized tomography (CECT) orbit showed exophthalmos with thickening of all the extraocular muscles, most prominent in bilateral inferior recti followed by medial recti and superior recti [Figure 2]a and b. CECT thorax was normal. Repetitive nerve stimulation test (RNST) of bilateral nasalis muscle revealed decremental response, more prominent in the right nasalis muscle, suggestive of myasthenia [Figure 3]a and b. Comparing the fifth action potential with the first action potential, there was a 49% decrease in the amplitude and 28% decrease in the area of the compound muscle action potential (CMAP) of right nasalis muscle. A 19% decrease in amplitude with a 24% decrease in area of CMAP of left nasalis was also noted. Any decrement of greater than 10% in considered significant, with the decrement in area considered to be more specific than that of amplitude in diagnosing myasthenia. [8] Electrodiagnostic screening for concomitant myopathy or neuropathy was unremarkable. The patient showed improvement in ptosis and external ophthalmoplegia with neostigmine test. Anti-acetylcholine receptor antibody (anti-AchR-Ab) level was elevated 1.46nmol/L (normal <0.5 nmol/L).{Figure 2}{Figure 3}

She was started on pyridostigmine (Myestin, VHB, Mumbai) initially 60 mg thrice daily which was increased to 60 mg four times per day. She also received carbimazole (Thyrocab, Abott, Mumbai) 10 mg thrice daily which was subsequently tapered and stopped after 2 years of therapy. Her ptosis improved and there was partial improvement in external ophthalmoplegia in all directions. Exopthalmos was not affected by the therapy. Eye symptoms improved with 2% hydroxypropylmethylcellulose eye drops (Viscomet, Sun, Mumbai). Last evaluated 2 years after the initial diagnosis, patient was clinically and biochemically euthyroid, ptosis had improved, marked improvement in ocular movements with mild residual external ophthalmoplegia in horizontal axis.

 Discussion



Restrictive extra ocular muscle weakness has been observed both in patients with TAO and ocular myasthenia, but ptosis is absent in TAO. [8] Ptosis in a patient with Graves' disease suggests the coexistence of myasthenia gravis. Orbicularis oculi weakness in combination with ptosis or external ophthalmoparesis is a strong indicator of myasthenia. [8],[9] The presence of exopthalmos and firm goiter in our patient made us suspect underlying autoimmune thyroid disease. She was clinically euthyroid, but biochemically sub-clinical hyperthyroid. Disease course along with thyroid scan and uptake ruled out thyroiditis. FNAC evidence of thyroid hyperfunction in the background of diffuse uptake on radio-iodine study and ocular involvement confirmed diagnosis of clinically silent Graves' disease. External ophthalmoplegia was disproportionately severe in our patient as compared to exopthalmos and eye symptoms of TAO. Mild ptosis and associated severe external ophthalmoplegia in absence of bulbar, neck muscles, and limb weakness made us suspect ocular myasthenia. Positive RNST of bilateral nasalis muscles and neostigmine test in presence of positive anti-AchR antibodies confirmed the diagnosis of ocular myasthenia. Neostigmine was used for stimulation as edrophonium is not available in this part of world.

RNST is not the best test for diagnosing myasthenia cause of its low sensitivity (60%). Single fibre EMG (SFEMG) is the most sensitive test for the diagnosis of neuromuscular diseases including myasthenia. [8],[9] However it is less specific than RNST. SFEMG was not necessary in our patient as RNST was diagnostic.

Fifty percent of patients presenting with ocular myasthenia develop generalized weakness within 6 months and up to 80% will generalize within 2 years. [10] Patient with ocular myasthenia without any progression for 2 years, are likely to have symptoms restricted to the ocular muscles thereafter. [10] Our patient had improvement of symptoms with pharmacotherapy, and till 2 years of follow-up she was asymptomatic and did not complain of any limb weakness. She did not receive any immunosuppressive therapy like corticosteroids as she had only ocular myasthenia which responded well to pyridostigmine. Corticosteroid therapy at this age is associated with significant morbidity including osteoporosis.

To summarize we presented a lady with ocular myasthenia with TAO who had subclinical Graves' disease who responded well to medical management. This case intends to highlight that TAO and ocular myasthenia can co-exist, and is a diagnostic challenge. Diagnosis is important as lack of treatment of even clinically silent Graves' disease can aggravate myasthenia.

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