Patients will often report symptom onset after consuming a large amount of alcohol and then sleeping in an unnatural position. Otherwise, patients may report some other mechanism by which compression would have been unnaturally placed on the upper medial arm or axilla. It is possible that patients may not provide this info until prompted, as it can go unrecognized as the inciting event. Symptoms can also begin several days after the initial insult, leading to a delayed presentation. Patients may report numbness, weakness, tingling, pain, or any combination of these.  On physical exam, patients may demonstrate a characteristic wrist drop, which results from the loss of extensor muscle function controlled by the radial nerve branches and preservation of the flexor muscles controlled by other nerves in the hand and arm. This leads to an inability to extend the wrist and fingers at the level of the metacarpophalangeal joints. Patients also lose the ability to extend the thumb, resulting in difficulty with opening the hand and grasping objects. Providers should be aware that patients can still extend their fingers at the level of the proximal and distal interphalangeal joints, as these are controlled by the ulnar nerve. Additionally, patients may exhibit loss of the triceps reflex, which is controlled by radial nerve innervation. Sensory deficits will often involve the posterior or lateral upper arm, with symptoms extending distally to affect the posterior forearm, posterior hand, and posterolateral aspect of the lateral three-and-a-half digits.[5][6]

The evaluation and diagnosis of Saturday night palsy are primarily clinical, and many patients that have a clear history and physical exam may not require further diagnostic measures. However, additional diagnostic tools can be helpful in evaluating alternative causes and complications as well as for predicting prognosis. Electromyography and nerve conduction studies are able to localize lesions anatomically, which can help differentiate between cervical radiculopathies, brachial plexopathies, and peripheral neuropathies. Ultrasound can be a low-cost, low-risk modality that can assist with visualizing the nerve and identifying areas of damage or disruption. It can also be highly beneficial in early identification of obvious nerve disruption and hastening early surgical intervention for these cases. MRI can provide fine detail that may not be visible on ultrasound and can also identify which muscles have been affected. It can also evaluate for additional disease processes, neurologic disorders, and soft-tissue masses. X-ray imaging can evaluate for fractures, dislocations, and bony tumors that may be the cause of nerve injury. A combination of several imaging modalities may be appropriate when considering a specific case.[1][7]

Treatment for Saturday night palsy is largely focused on physical rehabilitation. Physical therapy involves the use of a soft wrist splint that holds the wrist in extension. However, it is important to allow for full passive range of motion of the affected extremity during rehabilitation, which can be accomplished by using a dynamic splint. These measures can be supplemented with supportive care, including non-steroidal anti-inflammatory drugs (NSAIDs), systemic corticosteroids, steroid injections, and rest from vigorous use. Some novel treatment strategies involve the use of ultrasound to administer localized injections to speed recovery. Surgical management is reserved for severe injuries of the radial nerve or for cases in which the compression results from an intrinsic process such as a mass, bone spur, or cyst.[1][8]

The differential diagnosis is extensive and includes a wide range of processes that can lead to radial nerve compromise. This includes traumatic causes, with humeral fractures being a very common cause of radial nerve injury. Additionally, severe blunt trauma, crush injuries, puncture wounds, and stab wounds are other common causes. Anterior glenohumeral shoulder dislocation can rarely lead to radial nerve injury as well and should be considered in any patient with physical exam findings consistent with this. Iatrogenic injury can be seen in any surgery or injection involving anatomy associated with the path of the radial nerve. Internal compression by growing cysts, masses, tumors, muscle hypertrophy, and fibrinous tissue can also cause nerve palsy. Rarely, repetitive overuse and neurologic diseases can cause isolated palsies as well, with some patients even being found to have acute ischemic strokes after presenting with isolated symptoms.[4][9][10]

The prognosis for Saturday night palsy depends on the extent of the injury, which is determined by the force and duration of compression. Mild damage results in neuropraxia, a transient conduction block without nerve degeneration. This type of injury will almost always result in complete recovery. Moderate damage results in axonotmesis, characterized by axonal damage and Wallerian degeneration that can have incomplete or late recovery. Severe damage results in neurotmesis, characterized by complete axon degradation and Schwann cell death with a low chance of full recovery. Patients with this degree of injury will often need surgical intervention. The degree of damage can be difficult to determine based on electromyography alone, and prediction of prognosis can be difficult early on. Recovery is not rapid, with even mild cases resolving at the earliest in 2-4 months and often much longer.[1][4][11]

Complications can arise from the failure to consider a wide differential diagnosis, which can lead to missing severe disease or illness. It is important to determine the etiology of the radial nerve deficits, as management can change drastically from case to case. In the case of a true compressive Saturday night palsy, the main complication arises from the failure of recovery, which can be an indication for surgical exploration. Surgical options then include nerve grafting, nerve transfers, tendon or muscle transfers, and numerous other described techniques. As with most surgical procedures, there can be a wide set of additional complications related to intraoperative issues and post-surgical infections. Additionally, partial recovery is often achieved in these cases, and long-term disability can be a challenge. Prolonged and persistent physical therapy can be burdensome but important in regaining some functionality.[1] 

Patients should be counseled on preventing re-injury by not repeating the same mechanism, which led to the insult initially. The importance of physical rehabilitation should be emphasized to increase the chance of recovery. Patients should also be urged to follow up as scheduled to ensure that their treatment plan can be adjusted as necessary, especially in cases where early surgical intervention is warranted. It is also important for patients to continue following up regularly in cases where the prolonged delay to recovery may necessitate late surgical exploration and intervention.

The initial provider to evaluate a patient with Saturday night palsy should ensure they are thoroughly worked up to rule out alternative causes for a new-onset neurologic deficit. Furthermore, appropriate referral to a neurologist to plan for electromyography and additional diagnostic/therapeutic measures should be made. A referral to physical therapy should be made as well, and patients should be educated on supportive measures. There should be an established timeline in place to ensure that surgical intervention can be pursued early if deemed to be necessary, and appropriate surgical follow up should ensue in these cases. Patients in all cases should be given realistic expectations in terms of the recovery process, which may not be as straightforward as expected or desired. [Level 5]