Parkinson disease

What it is

Parkinson disease is a neurodegenerative condition that involves the progressive depletion of dopaminergic neurons in the basal ganglia, particularly the substantia nigra, whose role is motor inhibition. That loss shows as depigmentation of the substantia nigra pars compacta. Parkinsonism as a state is put down to loss of dopaminergic neurons and excess cholinergic activity.

Causes and risk

Women and men are hit at the same rate and the peak age is 50 to 60 years. MPTP, a contaminant in illegal drugs, is metabolized to MPP+, which is toxic to the substantia nigra. On the gait table the parkinsonian gait is put down to parkinsonism - Parkinson's disease, drug-induced, Parkinsons Plus - and, listed beside parkinsonism, to atherosclerotic pseudoparkinsonism.

How it presents

The cardinal symptoms are held in the word TRAP: 1) tremor, which is a resting pill-rolling tremor; 2) rigidity, which is cogwheel; 3) akinesia or bradykinesia; 4) postural instability. Around these sit the gait and posture: a shuffling, short-stepped gait with festination, a stooped posture with the large joints in a flexed position, arms adducted with reduced or absent arm swing while walking, hypomimia and seborrhea in the face, and micrographia in the hand. Common early symptoms are myalgia and arthralgia, hyposmia, depression and obstipation. The near condition to part it from is Lewy body dementia, which is characterized initially by dementia and visual hallucinations and only then by parkinsonian features, and which also carries fluctuating cognition and alertness and REM sleep behavior disorder. The naming rule given is that it is called Lewy body dementia when the cognitive and motor symptom onset is less than 1 year apart, and otherwise dementia due to Parkinson disease. The gait table sets out the parkinsonian walk feature by feature: hesitation, shuffling, loss of arm swing, short quick steps called marche a petit pas, festination, which is speeding up inadvertently, and retropulsion, which is falling backwards as the feet rush ahead. The other gaits it is read against are the antalgic gait, with less time spent on the painful limb; the Trendelenburg waddling gait of hip abductor weakness; the broad-based sensory ataxic gait with the patient looking at the feet, from peripheral sensory neuropathy or dorsal column loss; the broad-based cerebellar gait, high-stepping and looking carefully ahead, from a cerebellar lesion usually of the vermis; the hemiplegic gait, with the foot plantarflexed and the knee extended so the leg is abducted and swung in a lateral arc; and the high-stepping foot-drop gait of a common peroneal nerve palsy.