NR 569 Week 4 Discriminating Feature Brief Example

Thiamine Deficiency or a Posterior Circulation Stroke in an Unsteady Patient After Gastric Bypass: One Bedside Feature That Pulls the Pair Apart

Student Name

College of Nursing, Chamberlain University

NR 569: Differential Diagnosis in Acute Care Practicum

Instructor Name

Month Day, Year

Thiamine Deficiency or a Posterior Circulation Stroke in an Unsteady Patient After Gastric Bypass: One Bedside Feature That Pulls the Pair Apart

Why This Pair

The patient is 47 and was admitted nine weeks after a Roux-en-Y gastric bypass, having vomited for three weeks, been confused for four days and fallen twice. By the morning of hospital day 2 the list had narrowed to three entries, and two of them collide. Wernicke encephalopathy and a stroke in the posterior circulation can both produce confusion, unsteady walking and vomiting, and both can produce abnormal eye movements. The vomiting itself does not choose between them: it could be the cause of a thiamine deficiency or the result of a brainstem or cerebellar lesion. The patient's own complaint, legs that will not obey, raises both.

The two conditions call for different first moves. One needs high-dose thiamine before more glucose. The other needs urgent imaging and a stroke pathway. Treating thiamine deficiency is cheap and safe, so the brief is not deciding whether to give thiamine; it is deciding how hard to look for a stroke while doing so.

A Feature That Can Be Obtained Here

The feature this brief relies on is the symmetry of the eye movement findings, examined at the bedside with a penlight and a finger target. Specifically, I look at three things: whether nystagmus appears when the eyes hold a position to the left and to the right; whether each eye fully abducts toward the ear on that side; and whether one eye sits higher than the other when each is covered in turn.

This examination needs no equipment beyond a light, takes about three minutes and can be done on a general medical floor at any hour. That matters. A brief that relied on a finding only an MRI or a neuro-ophthalmologist can produce would describe the physiology correctly and still be useless at 3 a.m.

Thiamine deficiency tends to produce bilateral, roughly symmetric eye findings: nystagmus on gaze to both sides, often with weakness of abduction in both eyes. A lesion in the posterior circulation more often produces findings that favor one side: a skew deviation, nystagmus that is worse in one direction, or limb incoordination on one side. A review of thiamine deficiency describes nystagmus and bilateral sixth nerve weakness as among its common eye signs (Sechi & Serra, 2007).

Presence and Absence, Separately

The two directions of this feature are not worth the same, and the brief treats them separately.

If symmetric findings are present: bilateral gaze-evoked nystagmus with weakness of abduction on both sides, in a patient with weeks of vomiting after bypass surgery, moves thiamine deficiency to the top of the list. It does not remove stroke, because a midline brainstem lesion can produce bilateral signs, but it shifts the burden. In the criteria proposed for this diagnosis, eye signs are one of four features, and two are enough (Caine et al., 1997). This patient would then meet all four.

If one-sided findings are present: a skew deviation, or limb incoordination on one side, moves stroke up and calls for urgent imaging. A three-part bedside eye examination including a test for skew was more sensitive for stroke than early diffusion MRI in patients with acute vestibular symptoms (Kattah et al., 2009). That study enrolled patients with continuous vertigo, so I use it as support for the value of a skew deviation, not as a validated rule for this patient.

If eye movements are normal: the absence does very little. Fewer than one in five necropsy-proven cases of thiamine deficiency showed all three classic signs during life, and many showed none of the eye signs. Normal eyes leave both conditions on the list and push the decision to imaging.

The Feature in Time

Time works in two directions here. First, eye findings in thiamine deficiency can change quickly once thiamine is given; nystagmus and eye weakness are often the earliest signs to improve (Sechi & Serra, 2007). A repeat examination 24 to 48 hours after high-dose thiamine therefore becomes a second, independent use of the same feature: improvement points toward deficiency, while signs that stay fixed or worsen point back toward a structural lesion.

Second, the feature is only useful if it is examined before it changes. Thiamine was in last night's infusion, though at a low dose. If treatment at the full dose starts before anyone examines the eyes, the first finding may already be softened. The brief therefore asks for the examination before the next thiamine dose, and for the timing of every examination to be written beside its result.

What Each Outcome Would Change in the Orders

The brief exists to change what happens next, so each outcome is linked to an order. Symmetric findings: continue thiamine at the treatment dose, hold dextrose-containing fluids until thiamine has been given, correct the magnesium, since the enzymes that depend on thiamine also need magnesium to work, and request MRI as confirmation rather than as an emergency. One-sided findings: page the stroke team, obtain vascular imaging of the posterior circulation and note when the household last saw the patient at baseline. Normal eye movements: continue thiamine, request MRI without delay and repeat the eye examination after the next two doses.

In every outcome thiamine continues, because stopping it carries more risk than giving it to someone who turns out not to need it. What changes from one outcome to the next is the urgency of imaging and which team is called, and the brief keeps that difference visible so the order written at 16:00 matches the finding written at 15:30.

What the Examination Showed This Afternoon

I examined the patient at 15:30 on hospital day 2. On holding gaze to the left and to the right, horizontal nystagmus appeared in both directions. Neither eye fully abducted; each stopped a few millimeters short. There was no skew on alternate cover. Finger to nose was clumsy on both sides equally. These are symmetric findings.

Where the Brief Stops

This brief does not settle the diagnosis. Symmetric findings make thiamine deficiency the leading entry, but a midline brainstem lesion has not been excluded, and the brief does not argue whether MRI is still needed; that is the next document. Nor does it argue the thiamine dose, which follows the European guideline (Galvin et al., 2010) and does not depend on the result of this feature.

References

Caine, D., Halliday, G. M., Kril, J. J., & Harper, C. G. (1997). Operational criteria for the classification of chronic alcoholics: Identification of Wernicke's encephalopathy. Journal of Neurology, Neurosurgery & Psychiatry, 62(1), 51-60. https://doi.org/10.1136/jnnp.62.1.51

Galvin, R., Brathen, G., Ivashynka, A., Hillbom, M., Tanasescu, R., & Leone, M. A. (2010). EFNS guidelines for diagnosis, therapy and prevention of Wernicke encephalopathy. European Journal of Neurology, 17(12), 1408-1418. https://doi.org/10.1111/j.1468-1331.2010.03153.x

Kattah, J. C., Talkad, A. V., Wang, D. Z., Hsieh, Y.-H., & Newman-Toker, D. E. (2009). HINTS to diagnose stroke in the acute vestibular syndrome: Three-step bedside oculomotor examination more sensitive than early MRI diffusion-weighted imaging. Stroke, 40(11), 3504-3510. https://doi.org/10.1161/STROKEAHA.109.551234

Sechi, G., & Serra, A. (2007). Wernicke's encephalopathy: New clinical settings and recent advances in diagnosis and management. Lancet Neurology, 6(5), 442-455. https://doi.org/10.1016/S1474-4422(07)70104-7