Mohammed T. Abou-Saleh

344 PRINCIPLES AND PRACTICE OF GERIATRIC PSYCHIATRYKnowledge of the symptoms, signs and anatomic distributionof specific peripheral nerves is essential to recognize and diagnosethe mononeuropathies. These mononeuropathies are common inthe elderly. The most common chronic mononeuropathy is carpaltunnel syndrome (CTS), entrapment of the median nerve as itpasses under the carpal ligament at the wrist.Entrapment injury to the ulnar nerve is common in chronicillness, particularly in the elderly population. Psychiatric patientsrestricted to bed or a wheel chair use their elbows for support andoften compress the ulnar nerve at the olecranon notch, producinga ‘‘tardy ulnar palsy’’. The supine position, with the arms in aposition of mild flexion with the forearm pronated, exposes theulnar nerve to chronic pressure.The radial nerve innervates the extensor muscles for the fingers,wrist and elbow. The most common site of injury of the radialnerve is in the proximal portion of the nerve as it wraps aroundthe humerus. Injury often occurs when the patient is deeply asleepor unconscious (usually due to alcohol or sedation) while the armis held in abduction and lateral rotation. Injury results when thenerve is compressed by the head of a sleeping partner lying againstthe humerus (‘‘honeymoon palsy’’); or falling asleep with the armpropped over a bench, chair or bar (‘‘Saturday night palsy’’).The lateral femoral cutaneous nerve, a sensory nerve that arisesfrom the lumbar plexus, is often entrapped at the medial border ofthe anterior superior iliac crest, producing an acute or subacuteonset of numbness and a disagreeable prickly sensation over thelateral thigh (meralgia paresthetica). Sigmund Freud was one ofthree early describers of this and experienced it himself.Recognition is important, if only to avoid intervention to treatother conditions, such as lumbar radiculopathy.Peroneal nerve injury produces footdrop or loss of sensation inthe anterolateral surface of the foot. This can be subtle. The mostcommon cause of common peroneal nerve injury is crossing thelegs. Immobility is a predisposing cause, and depression, stroke ordementia is present among many patients.Sciatica is usually caused by a protruded lumbar disc affectingthe S1 root. However, the sciatic nerve is susceptible to injury atvarious sites in the buttocks causing identical symptoms and signs.Idiopathic inflammation of the brachial plexus (neuralgicamyotrophy, cryptogenic brachial plexopathy, Parsonage–Turner) predominantly affects the superior trunk of the brachialplexus. A deep aching pain in the axilla or shoulder is followedwithin a few days by weakness of muscles supplied by the superiorbrachial trunk.REFERENCES1. Massey JM. Neurology. In Crapo J, Hamilton M, Edgman S, eds,Medicine and Pediatrics in One Book, Philadelphia, PA: Hanley &Belfus, 1988; 425–58.2. Donofrio PD, Albers JW. Polyneuropathy: classification by nerveconduction studies and electromyography. AAEM Minimonograph34. Muscle Nerve 1990; 13: 889–903.