Terminology (Causes, Symptoms)

The modifiers acquired, sporadic, episodic, and idiopathic—how are they all related? Understanding the terms almost doesn’t help, because some people use the terms mutually inconsistently.

In this article, I use ataxia in its most general sense, as a cerebellar disease.

Causes

First, let’s consider the causes of ataxia. There are two categories: hereditary (i.e., genetic) and acquired (i.e., not genetic). Either you have ataxia because you inherited a genetic defect or acquired it some other way.

Acquired ataxia can be idiopathic (i.e., of unknown [root] cause), in which case (e.g.) your doctor may know from an MRI that your cerebellum is degenerating but not know why even after ruling out other possible causes, including bad genes.

Acquired ataxia can have a known cause, but there’s no commonly used antonym for idiopathic to mean this. Examples of this are cerebellar degeneration due to consumption of substances toxic to the cerebellum, or due to autoimmune issues.

Sporadic is often (but not always) a synonym for acquired. When it is a synonym, sporadic is describing the cause, not the symptom. Someone with sporadic ataxia has ataxia that has sporadic origins in them, not genetic origins. Many (most?) forms of sporadic ataxia are progressive (i.e., the symptoms are not sporadic) like most of the genetic forms.

Symptoms

Second, let’s consider the symptoms of ataxia. There are two categories here: sporadic and progressive. Be careful: there’s not an official antonym of sporadic; also, some (most?) with sporadic symptoms get progressively worse.

Yes, the term sporadic is overloaded: sometimes it means the cause in an individual is sporadic (i.e., not genetic), but it’s also used to describe symptoms when they occur sporadically (i.e., intermittently), even though the symptoms are probably also progressively worsening.

The episodic ataxias (EAs) are autosomal dominant (i.e., hereditary) but cause sporadic bouts of ataxia:

https://en.wikipedia.org/wiki/Episodic_ataxia

Let the games begin

The opposite of hereditary ataxia is acquired ataxia, and vice versa. If you are using acquired and sporadic as synonyms, then they are interchangeable. For example, the opposite of sporadic can be hereditary. This usage is safest when it’s clear from context that you are talking about the cause rather than the symptoms.

Here are some common uses of terminology that serve to confuse:

  • If you say you have sporadic ataxia with no additional context, then it’s impossible to know what you mean: are you talking about the cause or the symptoms?
  • In practice, some people equate sporadic ataxia and idiopathic ataxia, even though in theory this is wrong. They do this possibly because of lack of faith that nongenetic diagnoses can be truly definitive. Perhaps some suppose that if you have cerebellar ataxia for an unknown reason, then it’s only because your neurologist hasn’t gotten to the bottom of it yet, or perhaps your family history is not known. In that last case, running a complete battery of genetic tests may be prohibitively expensive. And so on.

Note that the term sporadic ataxia seems to imply cerebellar ataxia.

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