|Year : 2016 | Volume
| Issue : 2 | Page : 136-138
Myasthenia gravis: A rare presentation with absent ocular symptoms
Sandeep Lahiry1, Rajasree Sinha2, Dipak Bhowmik3
1 Department of Pharmacology, Institute of Post Graduate Medical Education and Research, Kolkata, West Bengal, India
2 Department of Pediatrics, Medical College, Dreamland Nursing Home, Kolkata, West Bengal, India
3 Medical Director and Incharge - Intensive Care Unit, Dreamland Nursing Home, Kolkata, West Bengal, India
|Date of Submission||01-Aug-2016|
|Date of Acceptance||18-Nov-2016|
|Date of Web Publication||13-Jan-2017|
Department of Pharmacology, Institute of Post Graduate Medical Education and Research, 244B, A.J.C. Bose Road, Kolkata - 700 020, West Bengal
Source of Support: None, Conflict of Interest: None
Myasthenia gravis (MG) is an autoimmune disorder in which there is antibody formation against acetylcholine (ACh) nicotinic postsynaptic receptors at the neuromuscular junction of skeletal muscles. Bulbar muscle paralysis is common, along with weakness in head and neck flexion. Extraocular muscle weakness or ptosis is the initial presentation in 50% cases and >90% cases during illness. It is usually treated with medications such as ACh-esterase inhibitors or immunosuppressants. Selected cases require thymectomy. Here, we present the case of a 32-year-old woman with MG, who presented with an unexplained respiratory failure in the absence of typical ocular symptoms. The diagnosis was based on clinical suspicion and specific laboratory tests. She was stabilized with mechanical ventilation and subsequently treated with immunoglobulin therapy and thymectomy.
Keywords: Acetylcholine, immunoglobulin, myasthenia gravis
|How to cite this article:|
Lahiry S, Sinha R, Bhowmik D. Myasthenia gravis: A rare presentation with absent ocular symptoms. J Curr Res Sci Med 2016;2:136-8
| Introduction|| |
Myasthenia gravis (MG) is associated with extraocular muscle weakness or ptosis in 50% of patients initially and >90% cases during illness. The disease can remain exclusively ocular in up to 16% cases, with nearly 85% cases progressing to generalized disease within 13 months after onset. There is the presence of myopathy-like proximal weakness involving limb musculature.
This case report highlights the importance of considering the possibility of MG even in the absence of classical neuromuscular symptoms in an acute setting. In an emergency room (ER)/Intensive Care Unit cases may present with unexplained symptoms, and quickly deteriorate into respiratory paralysis if not detected early.
| Case Report|| |
A 32-year-old woman presented to the ER with a 4-week history of generalized weakness and dysphagia. She was nondiabetic, nonhypertensive, and euthyroid.
While in the ER, she complained of breathlessness. Communication was difficult due to mild conductive hearing loss in her right ear. She had initially presented at a rural health center and was then transferred to our facility for further management.
On admission, she was conscious, alert and cooperative to verbal commands (Glasgow Coma Scale = 15/15). Her vital signs were stable though she complained of persistent breathlessness. Arterial blood gas analysis revealed compensated metabolic alkalosis. She was thin, with a body weight of 48 kg. General examination was unremarkable. Oral cavity and neck examination were within normal limits.
Chest auscultation indicated bilateral, basal, soft crackles and normal heart sounds. Chest skiagram revealed increased hyperlucency of basal zones and prominent bronchovascular markings. Abdominal examination was normal. Ultrasonography (abdomen) revealed mild hepatomegaly. Electrocardiogram and echocardiography were within normal limits.
Neurological examination revealed the absence of extraocular muscle weakness or ptosis. A mild degree of bilateral facial muscle weakness was present. The weakness of palatal muscles resulted in a nasal twang. Sensory and deep tendon reflexes were normal. Weakness in deltoids and extensors of the wrist and fingers were noted in upper extremity. In the lower extremities, weakness of hip flexors, quadriceps, and hamstrings, with the involvement of foot dorsiflexors or plantar flexors were also observed. Thorough skin and joint examination were undertaken to exclude autoimmune conditions (e.g., scleroderma, lupus, etc.). Hyperthyroidism was ruled out.
The absence of dysarthria, tongue atrophy or fasciculations excluded diagnoses of amyotrophic lateral sclerosis and paraneoplastic conditions. A magnetic resonance imaging screening (high cervical spine) later revealed partially desiccated C2–C3, C3–C4, and C5–C6 intervertebral disks. A mild posterior disc bulge at C6–C7 level was also found to be causing minimal indentation over the anterior thecal sac. No significant spinal stenosis was detected at any level. Cerebrospinal fluid examination was within normal limits. Specific blood tests including an autoimmune screen, antiganglioside antibodies, and tumor markers, which were.
Complete blood count, serum electrolytes, hepatic, and renal parameters were normal. Routine urine analysis was within normal limits. In spite of near normal respiratory parameters, the patient complained of persistent shortness in breath. A spiral computed tomography (CT) scan of the chest excluded the possibility of pulmonary embolism or mediastinal lesions like thymoma.
Mechanical ventilation support was initiated due to increased breathlessness, assuming bulbar paralysis. After intubation, she was hypotensive, needing low dose vasopressors for 3–4 h. She was started on intravenous fluids and piperacillin-tazobactam. Her hemodynamic measures improved with treatment, and she was afebrile within the next 48 h. Urine and endotracheal secretion cultures were sterile.
She had also developed left-sided facial weakness with slurring of speech and paraparesis, though CT brain was normal. Her weaning parameters were: vital capacity 500 ml, negative inspiratory force (NIF) 228 cmH2O (normal 235 cmH2O or less), and tidal volume 345 ml. The rapid shallow breathing index was 75. In spite of improved cardiorespiratory parameters, repeated attempts at extubation failed. These findings suggested respiratory muscle weakness. Since most neurodegenerative pathologies, space-occupying lesions, or intracranial infection were ruled out, MG was suspected.
Neurophysiological studies and acetylcholine (ACh) receptor antibodies were requested for confirmation. Nerve conduction velocity and electromyography studies confirmed bulbar MG showing a significant decremental response, jitter and blocking on repetitive nerve stimulation test (RNST). The ACh receptor antibody panel was positive for binding, blocking, and modulating antibody.
The patient was started on intravenous immunoglobulin (0.4 U/kg body weight) which was continued for 5 days, along with supportive therapy. Within the first 48 h of immunoglobulin therapy, her vital capacity improved from 500 ml to 1.4 L and the NIF increased to 280 cmH2O. She was gradually weaned off ventilation and was successfully extubated. On completion of 5 days of intravenous immnoglobulin, there was continued improvement of muscle strength during the rest of her stay in hospital. She was discharged after 2 weeks on steroids (tapered dose), azathioprine, and pyridostigmine.
| Discussion|| |
We present an atypical presentation of a relatively rare condition. This case illustrates the importance of considering neuromuscular disorders like MG in all age groups, even when the classical extraocular signs are absent in cases presenting with unexplained respiratory distress.
MG has a prevalence of 50–125 cases per million population. Individuals of all ages are affected, however, young women are predisposed with a peak incidence in the twenties. It is an autoimmune condition, and drugs like fluoroquinolones have been reported to exacerbate myasthenic weakness.
Clinical features include fatigue and muscle weakness, but reflexes are usually retained. Weakness increases with sustained muscle activity and is attenuated by rest and sleep. Cranial muscles are involved early, with diplopia and ptosis seen usually. Preserved sensation and reflexes are distinguishing factors from other neuropathies. Dysphagia can also be a feature, as seen in our patient. Generalized weakness occurs in 85% of patients. Muscle weakness tends to be more when the muscles are stressed, though strength improves with rest. Respiratory muscle weakness is common due to the involvement of diaphragmatic and intercostal muscles.
The basic pathophysiology involves a decrease in the number of ACh receptors at neuromuscular junctions. Acetylcholine-esterase (AChE) in the clefts rapidly hydrolyses the ACh and terminates its action on the muscle. Diagnostic tests needed to confirm clinical suspicion include AChE test, RNST, and ACh receptor antibody test. In the RNST, an electric current is delivered to the nerve, and action potentials are recorded on the surface of the muscle. The test is considered positive if there is decremental response of 15%. ACh receptor antibody testing is done by radioimmunoassay and is positive in 85% of patients with generalized MG. Edrophonium is the drug of choice for the AChE test because of its rapid onset and short half-life (few minutes).
Associated conditions, including thymic tumors and thyroid dysfunction (both hypothyroidism and hyperthyroidism) should be considered since both can exacerbate MG. Other possibilities are Lambert–Eaton syndrome, drug induced myasthenia, botulinum, and intracranial lesions.
Current treatment options for MG include AChE agents, surgical thymectomy, immunosuppression, and short term but fast-acting therapies such as plasma exchange and intravenous immunoglobulin. In general, AChE agents are used as the first line agents along with surgical thymectomy or immunosuppression.
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Conflicts of interest
There are no conflicts of interest.
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