Smoker’s disease is easily missed or misdiagnosed clinically, and we have found that most patients experience a considerable period of time from the onset of clinical symptoms to diagnosis, taking an average of two and a half years. Most patients are diagnosed with simple symptoms before diagnosis, and a few have been misdiagnosed with encephalitis, mitochondrial myeloencephalopathy, and gray matter heterotopia. There are several reasons why patients with smog are missed or misdiagnosed: 1. Smog clinical symptoms are complex and variable Some symptoms of smog, such as episodic limb numbness and weakness or paralysis of one limb, are easily thought of as vascular disease, but certain symptoms are difficult to think of directly in relation to vascular lesions, such as blurred vision, headache, dizziness and vertigo, episodic disorders of consciousness, limb twitching or mental retardation, etc. Therefore, if clinicians are Smoker’s disease lacks sufficient knowledge and does not arrange corresponding examinations related to cerebral arterial lesions for patients, such as transcranial Doppler ultrasound (TCD), magnetic angiography (MRA) and digital subtraction angiography (DSA), etc., it will lead to missed diagnosis. Many patients and even many doctors mistakenly believe that there is no problem as long as the head CT or MRI is normal, but this is actually not true for the diagnosis of smog. The first lesions in smog occur in the arterial ring at the base of the brain, and the artery does not progress from narrowing to occlusion in a short period of time, but usually over a long period of time, from a few years to several decades. Therefore, patients with only mild symptoms already have significant cerebral artery stenosis or occlusion, but at this time the cranial CT may be normal, and, without experience or careful observation, clinicians may also overlook the sparse vascularity of the large arteries at the base of the skull and the increased flow-void shadowing of the vessels at the base of the brain as shown on the cranial MRI-T2 phase. Some doctors have repeatedly performed cranial CT and cranial MRI examinations on patients, but have not examined the cerebral arteries once, resulting in patients with milder symptoms of smog being undiagnosed for a long time. 3. Some patients with cranial MRI changes are easily confused with other diseases. After the gradual occlusion of the skull base arteries in patients with smog, it leads to the formation of extensive intracranial and extracranial and cortical side branches, which causes changes in the blood supply range of the major cerebral arteries, therefore, the foci of cerebral infarction in some patients do not match the distribution range of cerebral arteries and are easily confused with encephalitis or mitochondrial myoencephalopathy. Such patients also often have many head MRIs but have not been examined for cerebral arteries. When stroke occurs in children, it is easy to look for the cause of stroke, but in adults, it is easy to conclude that cerebral arteriosclerosis and cerebral thrombosis are the cause of the stroke, so that many adults with smog are missed. More adults than children are found to have smog. Therefore, even adults with ischemic symptoms should be examined for cerebral arterial lesions, and some of these patients may have smog instead of atherosclerosis. While the common causes of clinical misdiagnosis or underdiagnosis of smog disease are mentioned above, we have found from our practice that while awareness of the complex clinical phases of smog disease is important, performing noninvasive cerebral artery lesion screening is even more decisive in detecting and diagnosing smog disease. Because cranial CT does not provide information directly relevant to the diagnosis of smoldering disease except for the detection of hemorrhagic or infarcted lesions, cranial MRI may provide valuable information such as abnormal basal vascular flow space shadowing, but in many cases only suggests ischemic or hemorrhagic lesions. The best way to diagnose smog is to visualize the arteries with DSA and MRA, but for screening smog, the non-invasive and inexpensive TCD is preferred. TCD is a non-invasive test for cerebral artery stenosis and occlusion. TCD has been used as a routine screening test for cerebral artery stenosis or occlusion in outpatients and wards for many years and has detected many patients with clinically suspicious or unanticipated smog. Many of these patients will not undergo invasive DSA or expensive MRA directly based on clinical presentation alone. In other words, TCD can screen out many patients with mild symptoms or atypical clinical symptoms. Therefore, TCD should be used as a routine screening method for cerebral artery stenosis and occlusion in neurology clinics and wards, so that more patients with smog disease can be diagnosed in a timely manner at the early stage of symptoms and may receive appropriate treatment before serious cerebral thrombosis or cerebral hemorrhage occurs.