Osteoarthrosis causing altered mental status: a case report

INTRODUCTION Cervical spondylosis as a cause of diaphragmatic weakness is an uncommon entity and has been reported primarily in the setting of cervical spinal cord compression. Cervical spondylosis most often causes respiratory failure from cervical myelopathy and damage to the ventral horn cells at spinal cord segments C3 to C5 from where the phrenic nerve arises. The manifestations are variable but there may be evidence of upper motor neuron signs and neurological deficits in the lower extremities along with Lhermitte's sign. Here we report a rare case of cervical spondylosis causing phrenic nerve root compression from foraminal narrowing at C3, C4 and C5, leading to lower motor neuron paralysis of the phrenic nerve and respiratory failure, in the absence of spinal cord involvement. CASE PRESENTATION An 87-year-old Caucasian man presented with recurrent episodes of hypercapnic respiratory failure and altered mental status requiring intubation. He was noted to have neurological deficits in his upper extremities with C5 radiculopathy deficits. An arterial blood gas showed a normal alveolar-arterial oxygen gradient with chronic respiratory acidosis, and pulmonary function testing showed restrictive lung mechanics with weakened neuromuscular apparatus and low maximum inspiratory and expiratory pressures. An extensive workup including electromyogram and magnetic resonance imaging showed evidence of phrenic neuropathy secondary to C3 to C5 neural foramina compression, from cervical spondylosis. He was treated conservatively with night-time bilevel positive airway pressure which rested his respiratory musculature with significant improvement. CONCLUSIONS Cervical spondylosis leading to phrenic nerve root compression is a rare and underreported cause of chronic respiratory acidosis and must be considered in the differential diagnosis of chronic hypoventilation, particularly in the elderly. This case illustrates how a simple arterial blood gas and calculation of the alveolar-arterial oxygen gradient can help in the workup of chronic respiratory acidosis by identifying causes of hypoventilation, which are associated with a normal diffusing lung capacity and thereby a normal alveolar-arterial oxygen gradient.