If the symptoms warrant, a beneficial and sustained response to levodopa or a dopamine agonist also gives a reasonably secure, although not entirely conclusive, indication of the presence of Parkinson disease (see further on). The other parkinsonian syndromes are for the most part changed only slightly or only for a few weeks or months by the drug. Conversely, although some experts disagree, we have adhered to the notion that complete resistance of the symptoms to l-dopa early in the illness makes the diagnosis unlikely. Furthermore, almost all patients with idiopathic Parkinson disease eventually acquire dyskinesias in response to l-dopa and the complete absence of this sign after approximately 3 to 5 years of use of the drug also brings the diagnosis into question.
Disorders simulating Parkinson disease The epidemic of encephalitis lethargica (von Economo encephalitis) that spread over Western Europe and the United States after the First World War left great numbers of parkinsonian cases in its wake. No definite instance of this form of encephalitis had been recorded before the period 1914 to 1918, and very few have been seen since 1930; hence, this type of postencephalitic parkinsonism is no longer a diagnostic consideration. However, a Parkinson-like syndrome has been described following other forms of encephalitis, particularly with Japanese B virus, West Nile virus, and eastern equine encephalitis. In the few cases caused by these viruses that we have observed, there has been fairly symmetrical rigidity, hypokinesia, and little or no tremor.
An “arteriopathic” or “arteriosclerotic” form of
Parkinson disease was at one time much diagnosed but we have never been entirely convinced of its reality, referring to damage to the substantia nigra as a result of vascular disease or to a syndrome that closely resembles Parkinson disease as a result of atherosclerotic white matter damage. Nonetheless, a number of authoritative clinicians are of the opinion that patients with a vascular cause have a predominantly “lower half” parkinsonism in which shuffling gait, stickiness on turning, and falling are disproportionate to other features. There is no tremor, and little or no response to l-dopa (see Winikates and Jankovic). MRI in such cases has shown substantial white matter changes in both cerebral hemispheres. In the few cases attributable to vascular parkinsonism that have come to our attention with autopsy material, there have been Lewy bodies in the appropriate locations. Pseudobulbar palsy from a series of lacunar infarcts or from Binswanger disease can cause a clinical picture that simulates certain aspects of Parkinson disease, but unilateral and bilateral corticospinal tract signs, hyperactive facial reflexes, spasmodic crying and laughing, and other characteristic features distinguish spastic bulbar palsy from Parkinson disease. Of course, the elderly parkinsonian patient is not impervious to cerebrovascular disease, and the 2 conditions overlap, but differentiating the predominantly gait or dementing disorders of widespread vascular brain damage from idiopathic Parkinson disease is not difficult.
Normal-pressure hydrocephalus can undoubtedly produce a syndrome resembling Parkinson disease, particularly in regard to gait and postural instability, and at times extending to bradykinesia; but rigid postures, slowness of alternating movements, hypokinetic ballistic movements, and resting tremor are not part of the clinical picture. The gait tends to be short-stepped but not shuffling and there is more of a tendency to retropulsion than there is in Parkinson disease. Sometimes a lumbar puncture gives surprising benefit, indicating hydrocephalus as the cause of the motor slowing and gait disorder.