Brachioradial Pruritus

Etiology

While not completely elucidated, current theories suggest brachioradial pruritus is a bifactorial process involving cervical nerve irritation and ultraviolet radiation (UVR) of the affected area.[4][5][6]  Most patients diagnosed with brachioradial pruritus have a positive imaging study with evidence of 1 or more cervical spine abnormalities. Imaging with x-ray, computed tomography (CT), or magnetic resonance imaging (MRI) of patients with suspected or diagnosed brachioradial pruritus revealed cervical spine abnormalities such as degenerative joint disease (DJD), cervical nerve impingement due to disk herniation, osteoarthritis, foraminal stenosis, and others. DJD has been reported as the most common cervical spine abnormality in patients with brachioradial pruritus.

Many authors suggest that cervical spine disease between C5 to C8 is causative. The dermatomes of the dorsolateral arms are C5 to C6, and a cervical spine abnormality with evidence of radiculopathy at these levels would be especially suggestive as a cause for brachioradial pruritus. Despite the high frequency of cervical spine abnormalities on imaging, nearly all patients with brachioradial pruritus imaged did not meet the criteria for cervical radiculopathy. Additionally, only a minority of patients diagnosed with brachioradial pruritus are imaged. This suggests that cervical radiculopathy not inclusive of radiologic criteria may be responsible for the high frequency of cervical spinal abnormalities in patients with brachioradial pruritus may simply be a confounding finding.

UVR is thought to be a contributing factor to brachioradial pruritus, and many patients report increased symptoms of brachioradial pruritus with sun exposure. The term brachioradial summer pruritus is also used in reference to the increased incidence of brachioradial pruritus during the warm summer months. A subset of histamine-sensitive C-fibers is responsible for the transmission of pruritus. Excessive UVR causes damage and a reduction of these C-fibers. Despite the reduction in cutaneous C-fiber number, increased pruritus is reported with UVR in patients with brachioradial pruritus. This pruritic response to a stimulus that does not normally cause pruritus is known as alloknesis. Many patients report relief of symptoms during the winter months and with sun protection, which supports the role of UVR as a trigger in brachioradial pruritus. The absence of either radiographically evident cervical nerve irritation or UVR does not preclude the diagnosis of brachioradial pruritus.

Epidemiology

Early isolated case reports suggested that brachioradial pruritus was more common in men. Results from later larger studies revealed that brachioradial pruritus is seen more commonly in women than men in a ratio of 3:1. The mean age at diagnosis is 59, but wide variations in age have been reported. Brachioradial pruritus is more common in lighter skin types, especially those with Fitzpatrick type I and type II skin, than in darker skin types. This factor further supports the role of UVR in the pathogenesis of brachioradial pruritus.

Histopathology

Brachioradial pruritus lacks characteristic histopathological features. Microscopic findings include actinic elastosis and decreased density of epidermal and dermal nerve fibers. Actinic elastosis correlates with a history of extensive UVR exposure. A decrease in the density of nerve fibers is seen with phototherapy treatments and would be consistent with UVR-induced brachioradial pruritus exacerbations during the sunny summer months.

History and Physical

Because pruritus has many etiologies, a thorough history is essential to avoid unnecessary testing and treatment delays. Brachioradial pruritus has a wide presentation area but is most commonly reported on the dorsolateral arms. Adjacent areas that may be affected are in the C5 to C6 dermatome and include the upper arms, shoulders, and neck. In addition to pruritus, patients may report pain, stinging, or tingling in the affected area.

Brachioradial pruritus is bilateral approximately 75% of the time.[7][8][9] Symptoms are usually present for 2 to 3 years before diagnosis. Patients are typically outdoor enthusiasts such as bikers, hikers, and tanners and may have an extensive history of sunburn. Despite the high frequency of cervical spine abnormalities seen on imaging in patients with brachioradial pruritus, retrospective studies report that very few patients had complaints of neck pain, cervical spine narrowing, or neck trauma.

The physical exam of the affected areas is not impressive and lacks primary cutaneous lesions. Secondary cutaneous lesions such as excoriations, prurigo nodules, or lichenification may be present due to excessive scratching. Confounding factors include coexistent chronic pruritic conditions, skin diseases, topical or systemic medications, and unusual presentations.

Evaluation

The ice-pack sign is considered pathognomonic for brachioradial pruritus. The test is simple and involves placing an ice pack on the affected area; the patient should report immediate improvement of pruritus that returns shortly after removing the ice pack. Evaluations beyond a thorough history and physical and the ice-pack test are typically unnecessary. Imaging, blood tests, and referrals to appropriate specialists may be required in recalcitrant cases. Imaging modalities such as x-rays, CTs, and MRIs usually are not required. If imaging of the cervical spine is desired, MRI is the preferred modality. Screening blood work for causes of chronic pruritus can be performed. Referral to neurology for further examinations may be appropriate if a neurological cause is suspected. Neurological examinations include cervical spine imaging and electromyography.

Treatment / Management

Treatment includes avoidance of UVR, topical medications, systemic medications, and, in select cases, surgery. Methods of UVR avoidance include reducing sun exposure, judicious use of sunscreen, and use of long-sleeved UV-protective clothing. This may be difficult for some patients with brachioradial pruritus, as many enjoy outdoor activities during the warm summer. Topical medications include capsaicin, mild steroids, anesthetics, antihistamines, and amitriptyline/ketamine. Earlier reports stated topical capsaicin was the most commonly prescribed initial therapy. A newer study reported the oral tricyclic antidepressant amitriptyline was the most commonly prescribed medication for brachioradial pruritus, although gabapentin may be more efficacious.

Other oral medications include risperidone, fluoxetine, chlorpromazine, and hydroxyzine. For unknown reasons, systemic antihistamine therapies are ineffective in brachioradial pruritus. Response to treatment was greatest in patients who rated their pruritus as severe and those who continued with longer treatments.[10][11][12] The sample size of most studies is small, and differences in the most prescribed and efficacious therapy vary. Surgery was reserved for patients with a correctable cervical spinal abnormality seen on imaging; very few patients fall into this category.(B3)

Differential Diagnosis

The differential diagnoses for brachioradial pruritus include the following:

• Neurotic excoriations
• Notalgia paresthetica
• Zoster sine herpete
• Atopic dermatitis