Tuesday, 23 October 2007

CT and Function

Although the use of CT scanning and MRI have transformed the world of doctoring for rapid diagnosis of conditions such as stroke and cancer, they do nothing to tell us how the patient is functioning.

As has been my experience in Japan, when a patient comes into hospital with some disorder that may indicate a cerebral problem, they are whisked into the waiting CT scanner for thieir cranial scan with or without contrast. Sometimes the neurological examination is bypassed as it is the belief that the scanner can give the answer to the problem.

To some extent, the use of scanning can give the answer, although not in its entirety.

A CT scan provides only pictures. Patients and their families are not interested in pictures that they bearly understand. They are interested on how the problem is going to affect them, for example, how it will affect their function.

The only way the function of a patient can be assessed is through examination.

Neurological examination is an indirect method of trying to understand what is going on in the head, spinal cord and muscles. It cannot tell us exactly what is going on, but it can tell us where a potential lesion exists and how it is affecting the function of the patient.

In fact, the use of physical examination of the neurological system and CT or MRI scanning complement eachother. However, a normal physical examination often does not require us to obtain a CT scan and a normal CT scan does not exclude an abnormality of function on examination.

Hence, physical examination is still a very much important part of a physicians armoury and it should not be skipped in favour of scanning the patient because important things can and will be missed.

For example, a patient admitted with sudden onset of speech abnormality and vomiting was found to have metastases on chest xray and hence, cerebral mets were suspected. CT was performed which indeed confirmed the mets. Great diagnosis......but the missing component was the functional ability of the patient.

When he was later examined by another doctor it was found that the patient had developed an homonymous hemianopia and unilateral upper limb weakness in addition to the speech abnormality. These differing neurological features suggest multiple areas affected. Moreover, such an examination revealed that the patient would be unsafe to drive (if feasible) because of the loss of vision and weakness of an upper limb. Following this, when one reviewed the physical findings to the CT result, it then made understanding the CT more easy as it could be understood that the patient's optic radiations to the occipital lobe had been disrupted by metastases and the speech abnormality was due to a pre-frontal lobe metastatic haemorrhage disrupting the pre-motor area in additon to the mutiple cerebellar lesions.

Acute treatment consisted of commencing dexamthasone to reduce the oedema. However, if no initial assessment of function through physical examination had been done, then there would be no way to fully know if the patient was improving or not. There needs to be a baseline admission examination.

In the UK, obtaining an emergency CT without the agreement of a radiologist is difficult. All emergency requests must be shown to the radiologist and for the decision to then be made by him or her. In my own experience, on occasions, radiologists have asked about the neurological examination and what you expect to find. If there is no physical examination or a poor physical examination performed, they will reject the request until an acceptable examination has been performed. Yes, you may think this is strict and overly controlling and to some extent it is, but it does ensure that the doctors examine their patient, think of the potential causes and what they will do if they find what they are looking for. It also reduces the unnecessary number of requests for head CT scans from anxious patients that think they have a brain tumour.

Unless a full neurological examination is performed with fundoscopy, the CT request may find itself coming back to you as rejected !! Obviously, this is case by case.

Hence, in the UK, physical examination is the mainstay of making diagnoses and in circumstances when a CT or MRI scan is needed, it will get done. In those cases where there is no clear reason for a CT but the patient wants it or the doctor wants reassurance, it is likely to be rejected by the radiologist. This cuts done on expenditure and unnecessary scanning.

The take home message is, always examine your patients neurology when such an examination is warranted and try and consider the places in the CNS or PNS which have been affected and where such problems localise to. This will then give you some idea of where you are expecting to find the problems when you eventually do scan the patient. The examination will provide you with the baseline functional status and with serial examination of the patient, it will tell you whether the patient is improving or not.

Basically, don't think that a scan is the replacement for clinical skill because it is not.

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