In neurological diagnosis, a properly taken history is one of the most important and helpful tools for the physician. Broadly, neurological disorders may be divided into four main pathological classes-vascular accidents, inflammations, neplasia and space occupying lesions and degenerations. Vascular accidents such as embolism, thrombosis, and hemorrhage come on abruptly, often within minutes to hours. In embolism, the neurological deficiency is maximal at the start, and tends to wear off with time. In thrombotic lesions often, there are warning transient ischemic attacks (TIAs) and the whole process may take a few to several hours. In hemorrhage, into the brain, sunset may be sudden or more prolonged. Initial symptoms such as severe headache, vomitin and sudden loss of consciousness may suggest a hemorrhagic stroke. Inflammatory lesions (eg, meningitis, encephalitis, and brain abscess) start acutely and they evolve over a period of days to weeks. In addition to the neurological features, they are usually accompanied by signs of systemic infection such as fever and toxemia.
generally, space occupying lesions have sub-acute onset and course progressing to the full fledged stage over a period of weeks to months. The progress may be steady or punctuated by periodic exacerbation caused by complications such as vascular thrombosis, hemorrhage or edema in the tumor. Degenerative lesions (eg, presenile dementia, spinocerebella degeneration) have a very insidious onset and progressive course extending over several years.
Higher functions : These include the level of consciousness, intelligence, memory, emotional state, and speech. These are all cortical functions. These are derived in cortical lesions.
Speech : speech disturbance may be due to defects in articulation (dysarthria), disturbance of structure and organization of language (aphasia), or disturbance of phonation (aphonia).
Dysarthria : There are three main types of dysarthria. In cerebellar disease, the speech is slow, deliberate, and scanning or staccato.
In bilateral pyramidal lesion occurring above the level of the brainstem, the speech is spastic. This is also known as pseudobulbar dysarthria. Such patients show evidence of upper motor neuron lesion of the cranial nerves supplying the muscles of the face, larynx, tongue, and respiration. Spaticity of the muscles supplied by the bulbar nucleari gives rise to slurring speech which may be compared to that of a drunken man. Other associated features such as dysphagia are present because of spasticity of the muscles of deglutition.
Lower motor neuron lesion of the muscles supplied by the brainstem nuclei gives rise to 'bulbar dysarthria'. The speech is slurred. Other evidences of lower cranial nerve palsies such as dysphagia and nasal regurgitation of fluids may coexist.
Aphonia : Inability to produce sounds while still able to make syllables and gestures is termed aphonia. This may be organic as a result of bulbar or pseudobulbar palsy or it may be a hysterical phenomenon.
Aphasia : Several parts of the cerebral cortex take part in speech function. These are the frontal lobe, temporal lobe, parietal lobe, occipital lobe, and the motor cortex. Aphasia is the inability to use language an this may involve speaking, writing and comprehending. The defect lies in the central mechanisms of speech. Aphasia has been classified differently by several authors. Ability to use language can be found to be made up of several discrete components which act together to produce normal speech.
1. Ability to use words in spoken speech- This consists of articulation, ability to put words together into phrases and grammatical constrictions (fluency), naming and accurate repetition of complex statements and concepts;
2. Summary of spoken speech;
3. Ability to read;
4. Ability to write; and
5. Ability to comprehend symbols, eg, mathematical symbols, musical symbols etc.
Defects of speech may give rise to fluctuations of articulation, fluency, verbal comprehension, naming, repetition, reading and writing. Lesions in different regions of the brain affect these modalities differently.
I. Anterior temporal lobe lesions (amnestic or Wernicke's aphasia): Disturbances of fluency verbal comprehension, repetition and writing.
2. Left frontal lesions- Articulation and fluency are mainly affected.
3. Left parieto-occipital regions- Impairment of reading (visual language functions).
4. Left parietal region- Writing is particularly impaired.
In right-handed individuals, the main speech center is in the left cerebral hemisphere which is termed the dominant hemisphere. The left cerebral hemisphere is dominant in many left-handed subjects as well.
In clinical practice, it is easier to assess articulation and fluency on the one hand and reading and writing on the other. In lesions anterior to the Rolandic fissure, the former are more, affected where in posterior lesions, the latter are more affected. These are mentioned before referred to as anterior (also called expressive0 and posterior (also called receptive) aphasias.
In lesions involving the motor cortex (left frontal and temporal lesions) due to disturbance in voluntary movement of the lips and tongue, orofacial apraxia may develop and may add an element of cortical dysarthria to aphasia. In anterior aphasias, the patient is unable to express words and words are substituted, eg, calling a pen, a knife, etc. In lesions of the left posterior temporal region. speech is made up only of asyllabic neuologies without producing any normal sense. This is called jargon aphasia. There is deliberate impairment of comprehension of spoken speech defects repetition of spoken words is possible, while in posterior defects this is not so.
In addition to spoken speech, testing the capacity to read and write gives important clues. The visual comprehension of language and spoken speech are tested by making the subject read loudly. Silent reading tests the comprehension of language. Inability to write is called dysgraphia. Repeated use of the same word inappropriately is called preseveration. Inability to understand and manipulate mathematic symbols is called acalulia. Expressive ideas through gestures and understanding them is known as gesture speech. Patients with Wernicke's aphasia (temporal lobe)) or with posterior aphasias do not understand gesture speech.
Apraxia : The inability to perform complex acts in the absence of motor or sensory paralysis is known as apraxia. Such subjects may be able to perform the components of such acts but are unable to complete them. Apractic subjects can not make use of objects, though their use will be recognized by them. For example the patient may know the use of a pencil, but when asked to write he may not be able to do so. Apraxia results from damage to left parietal Cortex, Parietal white matter of left or both hemisphere or the interhemispherical fibers through the corpus callosum.