Is Parkinson's disease typically difficult to diagnose?

Yes. It is often said that diagnosing PD is equal parts art and science. This is true for a number of reasons. First, there is no 'test' to confirm a diagnosis as this time. Also, the presenting symptoms can be extremely subtle in the early stages and there can be multiple possible causes for particular symptoms that muddy the water. Add to this the fact that almost every patient experiences PD in a different way (it is called the 'designer disease' for that reason) and progresses at a different rate and anyone can see the potential for confusion and/or misdiagnoses. This does not take into account a variety of closely related Parkinsonism diseases referred to as Atypical Parkinson's or Parkinson's Plus that share some PD symptoms making them difficult to diagnose until later in disease progression. These include Dementia with lewy bodies (DLB), Progressisve Supranuclear Palsy (PSP), Multiple System's Atrophy (MSA), Vascular Parkinsonism, Corticobasal Degeneration (CBD), and Drug-Induced Parkinsonism.
Some people take years to diagnose correctly for these reasons. That is why it is a good idea to work with a movement disorder specialist (MDS) who has received specialized education and training whenever possible. Additionally, an MDS with years of experience would be desirable. An experienced specialist will do a detailed physical exam and ask about family history, history of neurological symptoms or head trauma and what may seem like unrelated symptoms that indicate the potential for developing PD, like diminished sense of smell, constipation, sleep problems and mood disorders.
Another factor to keep in mind is that, if you are concerned about cognition/memory issues, not all movement disorder specialists have advanced training in this area. Since this a common symptom especially in advanced PD, all MDSs have a basic understanding, but only some have the level of expertise you would want if you have been diagnosed with mild cognitive impairment or Parkinson's dementia.

Speaking from a young onset perspective, Parkinson's disease can be very challenging to diagnose. Most people see their primary care doctor at the onset of symptoms. Many primary care doctors are not looking for PD in young people. This can lead to many tests and misdiagnosis. For example, I was 29 years old and had an active tremor (not the typical resting tremor) in my right hand. I was diagnosed with carpal tunnel syndrome and told to wear a wrist brace. Over time, my right leg began to tremor and my arm stopped swinging when I walked. My primary care doctor referred me to a Neurologist who definitively said I did not have PD. When my symptoms did not go away, I pursued other avenues for diagnosis. I was fortunate that my sister worked in a hospital on a Neurology floor and was told about Movement Disorder Specialists. After ruling out other diseases via MRI and blood work, I was diagnosed. I feel fortunate that my time to diagnosis was relatively short. I have friends that were of similar age that it took years and upwards of 10+ doctors to reach a diagnosis.
I believe as Parkinson's education increases and more patients see Movement Disorder Specialists, the time to diagnosis will shorten and patient care will increase.

My experience mirrors others who have already replied: it took me a while, and I diagnosed it (by diligent use of the web), primarily because no one - doctors of any type, including several neurologists - didn't have a clue! At the moment, my PCP couldn't spell what I deal with, I don't think. I'd replace him, but several predecessors were similarly uninformed. The elder President Bush was similarly afflicted, and, as we're both Texans, you would have thought some would have paid attention. Not!

Having. Lupus and as well as a rare movement disease,Orthostatic Tremor Syndrome made my diagnosis even more of a challenge for my medical team.So many similar symptoms occur in both of these diseases and mimic Parkinson’s as well. Originally I was also diagnosed with mild Parkinsonism . In August 2020, as I presented with additional symptoms, it was determined that I did indeed have Parkinson’s.I have a great deal of respect and gratitude for my Movement Disorder Specialists who explored all avenues and still have the challenge of deciding which one of my disorders is responsible for a new symptom. Hopefully as more research is done the time of onset and diagnosis will take less time and fewer tests will be necessary.