As a result of lower motor neurone degeneration, the symptoms of PMA include:

- atrophy

- fasciculations

- muscle weakness

Some patients have symptoms restricted only to the arms or legs (or in some cases just one of either). These cases are referred to as "Flail Arm" (FA) or "Flail Leg" (FL) and are associated with a better prognosis.

In contrast to amyotrophic lateral sclerosis or primary lateral sclerosis, PMA is distinguished by the "absence" of:

- brisk reflexes

- spasticity

- Babinski's sign

- Emotional lability

Motor neuron diseases affect either upper motor neurons (UMN) or lower motor neurons (LMN), or both:

A motor neuron disease (MND) is any of several neurological disorders that selectively affect motor neurons, the cells that control voluntary muscles of the body. They include amyotrophic lateral sclerosis (ALS), hereditary spastic paraplegia (HSP), primary lateral sclerosis (PLS), progressive muscular atrophy (PMA), progressive bulbar palsy (PBP) and pseudobulbar palsy. Spinal muscular atrophies (SMA) are sometimes included in the group by some neurologists but it is different disease with clear genetic cause. They are neurodegenerative in nature and cause increasing disability and eventually, death.

Migraine and migraine with aura are common comorbidities. However, comorbid migraine worsens some of the additional visual symptoms and tinnitus seen in "visual snow" syndrome. This might bias research studies by patients with migraine being more likely to offer study participation than those without migraine due to having more severe symptoms. In contrast to migraine, comorbidity of typical migraine aura does not appear to worsen symptoms.

Patients with visual "snow" have normal equivalent input noise levels: Visual snow is a poorly understood symptom. Patients report seeing "snow", much like the visual noise on a TV screen after transmission ends. Some hypothesize that what the patients see as "snow" is their own intrinsic visual noise. Dennis Pelli and others' measurements assess whether visual-snow patients have increased levels of intrinsic visual noise.

Visual snow, also known as visual static, is a proposed condition in which people see white or black dots in parts or the whole of their visual fields. The problem is typically always present and can last years. The severity of the "snow" differs; and it has been suggested that in some the condition may affect daily life, making it difficult to read, drive, or see in detail. The use of computer screens can exacerbate symptoms.

The cause is unclear. Typically it occurs in people with migraines. The underlying mechanism is believed to involve excessive excitability of neurons within the cortex of the brain. It is commonly confused with floaters, leading to misdiagnosis as well as underdiagnosis.

Medications that may be used include lamotrigine, acetazolamide, or verapamil. But these do not always result in benefits.