In the diagnosis of functional weakness and sensory disturbance, positive physical signs are as important as absence of signs of disease. Motor signs, particularly Hoover's sign, are more reliable than sensory signs, but none should be used in isolation and must be interpreted in the overall context of the presentation. It should be borne in mind that a patient may have both a functional and an organic disorder.
Symptoms considered "functional," "psychogenic," "medically unexplained," or "hysterical" account for up to one third of new referrals to neurology outpatient departments. Complaints of weakness or difficulty walking, often in combination with sensory disturbance, represent a significant subgroup of these symptoms. Despite their frequency in clinical practice. descriptions of the diagnosis and management of these problems are not easily found in textbooks of neurology. Although elements of the history may be helpful, physical signs are often of crucial importance in the diagnosis of functional weakness.
In this article, we describe what is known and what is not known about the physical diagnosis of functional weakness, functional gait disturbance, and sensory disturbance. Where evidence is available, we have referred to it. Otherwise, we have had to rely on our own clinical and research experience with these patients. We wish to emphasise the importance of the following two maxims:
* Look for positive evidence of a functional disorder as well as the absence of signs of organic disease.
* Be prepared to make two diagnoses in some cases: one of disease and one of varying degrees of functional weakness (or functional "overlay").
BEFORE THE PHYSICAL DIAGNOSIS
A careful history is essential. In particular, the presence of multiple symptoms, depression or anxiety (particularly panic), or a history of several previous functional symptoms or surgical operations without positive pathology raise the likelihood that the primary symptom is functional. (1) Childhood adverse experience, personality factors, having a model for the illness, a recent life event, secondary gain (financial and otherwise), and illness beliefs may all be relevant to management, but not enough is known about these factors to allow them to be used in making the diagnosis.
The history of the onset of the symptoms can be particularly helpful. Patients with functional weakness will often describe symptoms suggestive of dissociation at the onset--either occurring in combination with panic, a physical trauma (often minor), or spontaneously. In this context, "dissociation" refers to the weakening or loss of the normal sense of ownership of one's actions and sensations. Descriptions suggestive of dissociation include: "the leg felt as if it was not connected to me", "I felt far away", or "I was in a place of my own".
The physical assessment of functional weakness should begin as the patient gets up from their chair in the waiting room and end as they are leaving the consulting room (or the hospital). The primary objective is to look for evidence of inconsistency. It may be particularly helpful to watch the patient:
* Taking their clothes off or putting them on.
* Removing something from a bag and replacing it (for example, a list of medicines).
* Walking into the room as compared with walking out of the room (and sometimes out of the outpatient building).
Hoover's sign is the most useful test for functional weakness and the only one that has been subjected to scientific study with a neurological control group. (2 3) It is a simple, repeatable test which does not require skilled surreptitious observation. The test relies on the principle that virtually everyone, whether they have a disease or not, extends their hip when flexing their contra-lateral hip. This finding is thought to be a result of the crossed extensor reflex, described by Sherrington, (4) which enables normal walking, and is present even in decorticate animals. The test as described by Hoover in 1908 (5) can be performed in …