This illness develops abruptly in an otherwise healthy individual; it may also complicate an infection, an injection of vaccine or antibiotic, childbirth, surgical procedures of any type, or the use of heroin. Magee and DeJong, in 1960, and Tsairis and coworkers, in 1972, reported large series of cases and amplified a well-known clinical picture. The term neuralgic amyotrophy was applied to this symptom complex by Parsonage and Turner, who wrote extensively on the subject. Their term for the condition is appropriate, as the clinical and EMG findings suggest a lesion of the peripheral nerves of the shoulder girdle and upper arm rather than in the cords of the plexus. Actually, the site of the pathologic changes has not been established. Our patients have nearly all been adults, ranging from 20 to 65 years of age. Males may be more susceptible.
Beginning as an ache or deep burning in and around the shoulder that is typically centered over the deltoid, at the root of the neck or in the axilla, and suspected at first of being only a muscle strain, the pain rapidly becomes very intense and may include a component of burning. The onset can be remarkably abrupt and occasionally awakens the patient from sleep. It is made worse by movements that involve the muscles in the region and the patient searches for a comfortable position. Narcotics are usually required to suppress the pain. After a period of several days there is a rapid development of muscular weakness and thereafter, sensory and reflex impairment. With the development of weakness, the pain begins to subside. In a few cases, the neurologic disorder occurs with little or no antecedent pain. Possibly in some there is pain that is not followed by demonstrable weakness. A small proportion of cases are bilateral at the outset, or the opposite side is affected weeks later but most cases remain one sided.
Unlike restricted radicular lesions, which almost never cause complete paralysis of a muscle because of overlapping innervations, certain muscles involved in brachial neuritis, such as the serratus anterior, deltoid, biceps, or triceps, may be totally or almost paralyzed, sometimes in isolation (see later). Rarely are all the muscles of the arm involved (4 of 99 cases of Tsairis et al). Most of the neurologic deficits in our patients have been localized around the shoulder and upper arm. Either the biceps or triceps reflex may be abolished. In a few cases there has been an additional median, radial, anterior, or posterior interosseous nerve palsy that can be detected and isolated by EMG to a site distal to the plexus (see later). Affected patients usually have no fever, leukocytosis, or increased sedimentation rate. Occasionally there is a mild pleocytosis (10 to 50 white blood cells/mm3) and slightly increased protein in the CSF, but most cases have a normal formula and sampling of CSF is not necessary for diagnosis.
Recovery of paralysis and restoration of sensation are usually complete in 6 to 12 weeks, but sometimes not for a year or longer. In approximately 10 percent of cases there is residual weakness and wasting of the affected muscles and a similar number have had a recurrence some time later on the same or the opposite side. A number of our elderly patients with this condition have had little recovery of motor function over 5 years. In a series of 246 cases described by van Alfen and colleagues that may be consulted for descriptions of the many clinical variations of this illness, they found that a considerable proportion had chronic pain and residual weakness. (Their series included idiopathic and hereditary brachial pleoxopathy, of the type addressed in the next section.)