A clinical examination technique for mild upper motor neuron paresis of the arm

Recognizing subtle upper motor neuron arm paresis is fundamental to the neurologic examination.1 Although the pronator drift test is widely used, others have contributed observations: Souque (see reference 2) described abduction of all fingers in the outstretched paretic hand; Wartenberg3 observed finger spreading in a single patient asked to press down with his paretic hand; Alter4 described the digiti quinti sign (isolated little finger abduction with outstretched hands, palms downward). Although these signs are useful, there are inconsistencies concerning their elicitation and utility.

To achieve a rigorous examination technique, 50 consecutive patients (“training set”) with mild unilateral arm weakness were prospectively evaluated by the author. Mild weakness was defined as minimal reduction in strength inapparent to the patient’s family and coworkers but manifesting as subtle difficulty in routine activities. Patients were excluded if they had weakness from a peripheral nerve lesion and were included only after imaging demonstrated an appropriate CNS lesion. Of these 50 patients, four had no arm weakness on clinical examination—two of these had ipsilateral nasolabial fold flattening, and two had no signs. Thirty-eight had a positive pronator drift: 1) 35/38 showed concomitant mild detectable weakness with resistive strength testing, 3/38 had no weakness with resistive strength testing; 2) 34/38 showed pronator drift when the fingers were either together or apart, 4/38 showed drift only when the fingers were spread apart; 3) 28/38 showed a downward shift of the hand, 10/38 showed only slow wrist pronation. Eight patients had no pronator drift, but did demonstrate finger spreading: four showed spreading of all fingers, and four showed only little finger abduction. Of the four patients with little finger abduction, this occurred in all four with palms upward and in two with palms downward. Of the 38 with pronator drift, they all did so within 30 seconds (24/38 by 15 seconds; 33/38 by 20 seconds). In those with finger spreading, this always occurred within 13 seconds. The four patients with no signs did not develop pronator drift even after 60 seconds. Eight patients had obvious arm weakness rendering pronator drift or resistive strength testing unnecessary for arm weakness detection.

Based on these data, the following examination technique was devised. With eyes closed (precluding visual compensation), the patient (seated or standing) holds both arms outstretched in front; the elbows and wrists are extended, and the hands are open with the palms supinated and pointed upward. Initially, the patient is asked to keep his or her fingers together for 15 seconds. Next, the patient spreads the fingers apart and is observed for an additional 15 seconds. Thus, the technique has two equal observation phases: fingers together (Phase I) and fingers apart (Phase II). During Phase I, there are two indicators of upper motor neuron weakness: a) little finger abduction or b) finger spreading. During Phase II, there are two indicators: a) slow wrist pronation with slight elbow flexion or b) downward and lateral drift of the hand. Phase II indicators may occur during Phase I observation.

This technique was validated by being applied to the next 25 consecutive patients (“test set”) presenting with the same inclusion/exclusion criteria. Three subjects had little finger abduction (Ia), one had finger spreading (Ib), six had hand pronation (IIa), and 14 had arm drift (IIb). One had no signs.

During Phase I, little finger abduction was better seen when the outstretched hands were palms up (opposite to the quinti digiti sign). During Phase II, there was improved drift elicitation when the fingers were spread, rather than together. Pronator drift always occurred within 30 seconds and did not require a full minute.5 This overall examination technique does not support the notion that little finger abduction → finger spreading → hand pronation → arm drifting is an observable continuum.

Care must be taken to avoid false positives: with ulnar nerve injury, little finger abduction may occur; in cerebellar disease, an outstretched arm may drift downward and outward; in proprioceptive disorders, an outstretched arm may elevate. A control group of 50 patients (mean age 68 years) with no arm weakness complaints and with no imaging abnormalities was evaluated: 49/50 had no pronator drift, 1/50 had little finger abduction.

This method of developing a clinical examination technique using a training set and a test set for prospective validation is unique; signs are normally described in a small group of patients on a retrospective ad hoc basis. Modifying the time-honored neurologic examination for improved reliability and quantifiability is not commonly pursued. However, the use of therapeutics whose administration is influenced by the presence of neurologic signs may render this a necessary pursuit.