An early treated neuralgic amyotrophy with bilateral phrenic nerve involvement with a favorable outcome
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.181578
Source of Support: None, Conflict of Interest: None
Neuralgic amyotrophy (NA) is an uncommon disease first described by Parsonage and Turner in 1948. The characteristic symptoms include acute shoulder pain followed by profound weakness in the upper extremities of the C5–C6 innervated muscles. NA manifests mainly unilaterally, usually involving the upper cervical plexus and is rarely reported to be additionally involving other adjacent nerves. The pathogenesis of NA remains unknown, but immunologic factors are considered to play an important role. Although the natural course of this disease is favorable, it resolves with prolonged chronic pain and mild paresis for several years. We report a rare case of a symmetric NA with bilateral phrenic nerve involvement that showed complete recovery after 3 months.
A 59-year-old man presented with acute shoulder pain followed by asymmetric arm weakness after a strenuous hiking. He also complained of orthopnea, and was unable to sleep in supine position. He had no history of preceding infection, recent vaccination, or trauma. The routine neurological examination showed no abnormalities of his cranial nerve function. His motor examination showed bilateral shoulder abduction weakness of Medical Research Council (MRC) Grade 3. He also had MRC Grade 4 weakness of the internal and external rotators of both arms that was more severe on the left side. Except for decreased deep tendon reflexes in his biceps, the other deep tendon reflexes were normal.
The laboratory tests performed to exclude autoimmune and infectious causes were unremarkable including the cerebrospinal fluid study. The nerve conduction study was compatible with bilateral upper trunk plexopathy with markedly decreased or unobtainable sensory nerve action potentials in bilateral lateral antebrachial and axillary nerves. The needle electromyography study showed active denervation potentials in bilateral deltoid, supraspinatus, infraspinatus, rhomboid, and teres minor muscles.
Interestingly, the patient complained of severe orthopnea, and, therefore, a cardiac echocardiography was also performed which was deleted to be normal. The pulmonary function tests were performed in both seated and supine positions. During the seated position, the tests were within normal limits, but on lying down, there was a significantly decreased forced vital capacity and forced expiratory volume, which were completely reversible [Figure 1]b and [Figure 1]c. The phrenic nerve conduction study was additionally performed and showed significantly reduced compound motor action potentials on both the sides. We also performed a videofluoroscopy that demonstrated bilateral phrenic nerve palsy [Figure 1]d. The brachial plexus magnetic resonance imaging showed a mild asymmetric hypertrophy prominent in the left upper brachial plexus, without significant contrast enhancement [Figure 1]a.
He was finally diagnosed as bilateral NA with bilateral phrenic nerve involvement within 1 week from the symptom onset. The patient was treated with 1000 mg of solumedrol intravenously for 5 days and continued with prednisolone 60 mg daily with stepwise dose reduction. Dramatic improvement was observed in his shoulder pain and orthopnea after 1 month of treatment, and his weakness recovered completely after 3 months [Figure 1]e.
NA is a rare neurologic disease that usually affects the upper trunk of the cervical plexus. The incidence is approximately 1.64 in 100,000, and it is prevalent in the third and sixth decades of life with a male predominance. NA usually involves the muscles innervated by C5–C7 nerve roots, and motor nerves are more frequently affected, compared to sensory nerves.
Acute neuropathic shoulder pain is the most common symptom in the early stage of the disease, and starts within a few hours lasting for upto 1–2 weeks. However, one-third of the patients eventually require long-term treatment to ameliorate pain. The prognosis of NA is known to be benign, and a large retrospective study illustrated a favorable natural course and prognosis with neurological improvement in 36% of the patients after 1 year, in 75% by the end of the 2nd year, and in 89% of patients after the 3rd year from the onset of the disease. However, another study showed that a third of the patients continued to suffer from chronic pain and majority of the patients exhibited persistent neurologic deficits even after 6 years of follow-up with a time discrepancy of approximately 10.5 weeks between the symptom onset and the establishment of the correct diagnosis. Therefore, the prognosis of NA is still debatable and the existence of time discrepancy could be an important causal factor responsible for residual neurologic deficits.
NA is rarely reported to additionally involve other motor nerves besides the brachial plexus. There are a few reports of NA that involved the lumbosacral plexus, recurrent laryngeal nerves, and phrenic nerves.,, Among these, phrenic nerve involvement has been rarely reported. The involvement has usually been unilateral, causing only a mild dyspnea, unlike in our case, which was bilateral, thereby causing severe orthopnea, with a paradoxical respiratory movement that was aggravated in the supine position. This rare involvement of the phrenic nerves in NA can be explained by the anatomy of the phrenic nerve, as it rises from the C3 to C5 nerve roots. With progression, NA, which classically involves the upper brachial plexus, can also affect the phrenic nerves. Gregory et al., showed that when NA was associated with phrenic nerve involvement, the recovery was poorer and more time was required to recover from it compared to the recovery from other neurologic deficits. This can be partly explained by the long length of the phrenic nerve that takes time to regenerate.
Unfortunately, there is no treatment that has been proven to reduce the neurologic impairment of NA, and there is only anecdotal evidence that early corticosteroid treatment may improve pain and hasten recovery in some patients. However, our case is of importance as it provides evidence that an early institution of steroid treatment can still be an effective option of treatment resulting in a markedly favorable outcome.
Our case broadens the clinical manifestations of NA. Thus, NA should be considered as an important differential diagnosis even when the patients complain of orthopnea. This can be achieved by conducting the phrenic nerve conduction study simultaneously with the routine nerve conduction study. The favorable outcome after establishment of an early diagnosis in our case suggests that steroid treatment can be an efficient option of treatment. Further clinical trials are required to elucidate the efficacy of steroids in the early stages of the disease.
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