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Most of the symptoms of myasthenia gravis are shared with other disorders of neuromuscular function. This can lead to problems diagnosing the condition until other suspects have been systematically ruled out. Abbott (2010) reports on one such case involving a 41-year-old man who presented at the emergency department (ED) of a small central Maine hospital complaining of “shortness of breath, neck and upper spine pain, difficulty holding his head up, and shoulder and upper arm weakness. He stated, ‘They told me I had Bell’s palsy, but I’m afraid I’ve had a stroke’” (Abbott, 2010). Indeed, the man had been seen five weeks earlier at the same ED suffering from some of the same symptoms, which had led to the initial diagnosis of Bell’s palsy that he mentioned upon being seen again at the hospital.
The patient reported several symptoms beyond those quoted above. This included ptosis of the left eyelid, fatigue caused by chewing, stuttering when tired, and intermittent diaphoresis (sweating). As seen in Figure 1, ptosis is a common symptom of myasthenia gravis and is often asymmetric, with one eye being more severely affected than the other. Examination of the patient revealed decreased muscle tone and abnormal neuromuscular reflexes. After speaking for a while, the patient exhibited signs of slurred speech and mild stuttering. The patient was discharged with instructions to return the next day for a brain MRI scan. However, the scan didn’t occur because the patient came back in an ambulance with continued complaints of shortness of breath as well as worsening neuromuscular abnormalities. Blood was drawn, and a lumbar spinal tap was performed to test for signs of infection (either systemic or CNS-related) or other kinds of diseases or disorders; however, all tests came back normal.
Figure 1 Appearance of ptosis in a patient with myasthenia gravis Note that this photo is meant to be illustrative since it depicts a different patient than the one described in the present case study. (© Shero/Medical Images)
With nothing beyond the neuromuscular symptoms to go on, the doctors considered a number of diagnostic possibilities: amyotrophic lateral sclerosis (Lou Gehrig’s disease), Guillain–Barré syndrome, multiple sclerosis, poliomyelitis, and myasthenia gravis. Through the process of differential diagnosis (discerning among multiple diagnostic possibilities by ruling alternatives out, one by one), most of these disorders were considered unlikely. Yet a positive diagnosis had not yet been reached. Consequently, the patient was transferred by ambulance to a larger hospital 60 miles away and subjected to a more thorough neurological workup. Among the new tests performed was a test for the presence of circulating antibodies against the muscle cholinergic receptor. A positive result from this test led to the diagnosis of myasthenia gravis. The medical team immediately instituted a treatment regimen that consisted of pyridostigmine to inhibit AChE, immunosuppressive therapy to reduce the continued immune attacks on the muscle receptors, and the anti-inflammatory steroid hormone prednisone. Prednisone was administered because of the presence of inflammation at the neuromuscular junction, which contributes to the muscle breakdown process.
Readers may wonder why the cholinergic receptor antibody test wasn’t performed earlier in the patient’s medical history. In response, we note that this is not a standard test in an initial neurological exam, and it was reasonable for the physicians to rule out other disorders before conducting this specific diagnostic test. On the other hand, because the patient lived in a rural area and first visited a small hospital, he initially lacked access to the higher level of medical expertise that was available at the larger hospital to which he was transferred. This expertise undoubtedly played an important role in reaching the correct diagnosis and developing an appropriate treatment plan.
Reference
Abbott, S.A. (2010). Diagnostic challenge: Myasthenia gravis in the emergency department. Am. Acad. Nurse Pract., 22, 468–473.