Harrison's Manual of Medicine
MONONEUROPATHY
Clinical Features
Mononeuropathies are usually caused by trauma, compression, or entrapment. Sensory and motor symptoms are in the distribution of a single nerve—most commonly the ulnar or median nerve in the arm or peroneal (fibular) nerve in the leg. Intrinsic factors making pts more susceptible to entrapment include arthritis, fluid retention (pregnancy), amyloid, hypothyroidism, tumors, and diabetes mellitus. Clinical features favoring conservative management of median neuropathy at the wrist (carpal tunnel syndrome) or ulnar neuropathy at the elbow include sudden onset, no motor deficit, few or no sensory findings (pain or paresthesias may be present), and no evidence of axonal loss by EMG. Surgical decompression is considered for chronic mononeuropathies that are unresponsive to conservative treatment if the site of entrapment is clearly defined. The most common mononeuropathies are summarized in Table 196-3.
| SYMPTOMS | PRECIPITATING ACTIVITIES | EXAMINATION | ELECTRO-DIAGNOSIS | DIFFERENTIAL DIAGNOSIS | TREATMENT | |
|---|---|---|---|---|---|---|
| Carpal tunnel syndrome | Numbness, pain, or paresthesias in fingers | Sleep or repetitive hand activity | Sensory loss in thumb, second, and third fingers Weakness in thenar muscles; inability to make a circle with thumb and index finger Tinel sign, Phalen maneuver | Slowing of sensory and motor conduction across carpal tunnel | C6 radiculopathy | Splint Surgery definitive treatment |
| Ulnar nerve entrapment (UNE) at the elbow | Numbness or paresthesias in ulnar aspect of hand | Elbow flexion during sleep; elbow resting on desk | Sensory loss in the little finger and ulnar half of ring finger Weakness of the interossei and thumb adductor; claw-hand | Focal slowing of nerve conduction velocity at the elbow | Thoracic outlet syndrome C8–T1 radiculopathy | Elbow pads Avoid further injury Surgery when conservative treatment fails |
| UNE at the wrist | Numbness or weakness in the ulnar distribution in the hand | Unusual hand activities with tools, bicycling | Like UNE but sensory examination spares dorsum of the hand, and selected hand muscles affected | Prolongation of distal motor latency in the hand | UNE | Avoid precipitating activities |
| Radial neuropathy at the spiral groove | Wrist drop | Sleeping on arm after inebriation with alcohol—“Saturday night palsy” | Wrist drop with sparing of elbow extension (triceps sparing); finger and thumb extensors paralyzed; sensory loss in radial region of wrist | Early—conduction block along the spiral groove Late—denervation in radial muscles; reduced radial SNAP | Posterior cord lesion; deltoid also weak Posterior interosseous nerve (PIN); isolated finger drop C7 radiculopathy | Splint Spontaneous recovery provided no ongoing injury |
| Thoracic outlet syndrome | Numbness, paresthesias in medial arm, forearm, hand, and fingers | Lifting heavy objects with the hand | Sensory loss resembles ulnar nerve and motor loss resembles median nerve | Absent ulnar sensory response and reduced median motor response | UNE | Surgery if correctable lesion present |
| Femoral neuropathy | Buckling of knee, numbness or tingling in thigh/medial leg | Abdominal hysterectomy; lithotomy position; hematoma, diabetes | Wasting and weakness of quadriceps; absent knee jerk; sensory loss in medial thigh and lower leg | EMG of quadriceps, iliopsoas, paraspinal muscles, adductor muscles | L2–4 radiculopathy Lumbar plexopathy | Physiotherapy to strengthen quadriceps and mobilize hip joint Surgery if needed |
| Obturator neuropathy | Weakness of the leg, thigh numbness | Stretch during hip surgery; pelvic fracture; childbirth | Weakness of hip adductors; sensory loss in upper medial thigh | EMG—denervation limited to hip adductors sparing the quadriceps | L3–4 radiculopathy Lumbar plexopathy | Conservative management Surgery if needed |
| Meralgia paresthetica | Pain or numbness in the anterior lateral thigh | Standing or walking Recent weight gain | Sensory loss in the pocket of the pant distribution | Sometimes slowing of sensory response can be demonstrated across the inguinal ligament | L2 radiculopathy | Usually resolves spontaneously |
| Peroneal nerve entrapment at the fibular head | Footdrop | Usually an acute compressive episode identifiable; weight loss | Weak dorsiflexion, eversion of the foot Sensory loss in the anterolateral leg and dorsum of the foot | Focal slowing of nerve conduction across fibular head Denervation in tibialis anterior and peroneus longus muscles | L5 radiculopathy | Foot brace; remove external source of compression |
| Sciatic neuropathy | Flail foot and numbness in foot | Injection injury; fracture/dislocation of hip; prolonged pressure on hip (comatose pt) | Weakness of hamstring, plantar, and dorsiflexion of foot; sensory loss in tibial and peroneal nerve distribution | NCS—abnormal sural, peroneal, and tibial amplitudes EMG—denervation in sciatic nerve distribution sparing glutei and paraspinal | L5–S1 radiculopathies Common peroneal neuropathy (partial sciatic nerve injury) LS plexopathies | Conservative follow-up for partial sciatic nerve injuries Brace and physiotherapy Surgical exploration if needed |
| Tarsal tunnel syndrome | Pain and paresthesias in the sole of the foot but not in the heel | At the end of the day after standing or walking; nocturnal | Sensory loss in the sole of the foot Tinel sign at tarsal tunnel | Reduced amplitude in sensory or motor components of medial and planter nerves | Polyneuropathy, foot deformity, poor circulation | Surgery if no external cause identified |
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