Q1: What is the mechanism of this patient’s breathlessness and how would you confirm this?

This man is breathless due to bilateral diaphragmatic paralysis, which causes profound orthopnoea and paradoxical abdominal motion, unlike other common causes of breathlessness. The clinical picture differs from orthopnoea of cardiorespiratory origin in its strikingly rapid onset on lying flat, with rapid and complete recovery on sitting up. Paradoxical abdominal motion (that is, movement of the abdominal contents inward during inspiration) is an important physical sign of diaphragmatic weakness. Therefore, in the absence of other signs indicating a respiratory or cardiovascular cause for the orthopnoea, a careful search for paradoxical abdominal motion is important.

Fluoroscopic screening of the diaphragms can be used to confirm bilateral paresis and paradoxical movement.

Q2: What is the likely clinical diagnosis. How would you try to establish this?

Bilateral diaphragmatic weakness is most often observed in the context of generalised neurological illnesses affecting muscle (for example, polymyositis or muscular dystrophies), neuromuscular transmission (for example, myasthenia gravis), inflammatory polyneuropathies (for example, Guillain-Barré syndrome), or anterior horn cell disease.¹ However, involvement of the diaphragm in association with the rapid onset of orthopnoea, asymmetric or unilateral shoulder pain, and patchy weakness of arm and shoulder girdle muscles should alert the clinician to the correct diagnosis of brachial neuritis (neuralgic amyotrophy). Accurate, prompt diagnosis requires a high index of suspicion and awareness of the clinical features, and is important for starting appropriate management and avoiding unnecessary investigations or treatment.

Brachial neuritis is characterised clinically by pain, atrophy, weakness, and variable sensory loss around the shoulder girdle.² Typically, sudden deep pain around the shoulder girdle—described as sharp, aching, boring, or throbbing—is associated with muscle weakness either simultaneously or after a variable period of several days to weeks. Commonly affected muscles include the deltoid, serratus anterior, spinati, biceps, triceps, and wrist and finger extensors; sensory deficit is usually less conspicuous. The annual incidence is approximately 1.64 per 100 000.³ Men are more commonly affected, with the highest prevalence in the 20–50 year age group.² Unilateral or bilateral diaphragmatic weakness is found in about 7% of patients, and may dominate the clinical presentation.⁴ The precise location of the lesion, and its pathogenesis remain puzzling; viral and autoimmune processes have been suggested but not confirmed.

Nerve conduction studies (NCS) and electromyography (EMG) are the most helpful diagnostic tests; extensive needle electrode examination may be required. In this patient NCS/EMG revealed normal sensory and motor conduction velocities, but no evidence of a neuromuscular junction transmission disorder. There was complete denervation of the right deltoid muscle, and milder neurogenic changes in the right supraspinatus, biceps, and brachioradialis. The EMG findings of active, patchy denervation strongly favoured the diagnosis of brachial neuritis, and helped to exclude peripheral nerve or root involvement.

Routine laboratory studies on blood, and examination of the cerebrospinal fluid are unremarkable in brachial neuritis. Magnetic resonance imaging may be helpful in excluding local neoplastic, infiltrative, traumatic, and musculoskeletal conditions.

Q3: What is the treatment and prognosis for this patient?

Accurate and prompt diagnosis of brachial neuritis can help to avoid potentially hazardous investigations and treatment. Treatment is mainly supportive, including analgesics, physiotherapy, and reassurance. Corticosteroids (for example, prednisolone, 60 mg daily tapering over two weeks) may be given to accelerate recovery and reduce pain, but they have not been shown to clearly influence the course of the illness. The clinical outcome with diaphragm involvement is variable. Some degree of recovery is usual but may be slow or incomplete.⁵ The patient described was treated conservatively with analgesics and physical therapy, and advised regarding sleeping posture. Ten months after discharge, he remained well with only mild orthopnoea.

Final diagnosis

Brachial neuritis (neuralgic amyotrophy).