Toxic neuropathies are not as easy as one may think. There is no other kind of neuropathy for which history and neurological examination are so crucial for the diagnosis, as no definitive diagnostic tests are available. In addition, it is important to review the medical records in detail and get collateral history, as patients often mistake the dates when medications started or stopped, or do not disclose to you the full story.

Three essential principles:

1. Symptoms must be time-associated with the medication or exposure to the toxin. The onset of symptoms often correlates with:

-Cumulative dose (e.g., many chemotherapy agents like paclitaxel or cisplatin show dose-dependent toxicity)
- Duration or time of exposure (e.g., acute glue-sniffing hexane; chronic use of metronidazole or nitrofurantoin),
- Time since initiation (e.g., some drugs cause neuropathy within weeks to months of starting therapy). Sometimes neuropathy may worsen or symptoms start after stopping the drug (known as “coasting”), particularly seen with agents like vincristine and cisplatin. Coasting should not last for more than 3 months.

2. After cessation of the exposure, the neuropathy must improve (after a few months) or not progress (except for some chemos that cause coasting). If this does not happen, alternative causes should be considered. ,

3. When re-exposed to the offending agent, the neuropathic symptoms usually worsen—a very common phenomenon in chemotherapy-induced peripheral neuropathy.

1/x Toxic neuropathies usually present as a length-dependent sensory predominant axonal peripheral neuropathy, but may have severe motor involvement and even present like GBS.

Common causes include:
•Chemotherapy (e.g., vincristine, platinum-based, paclitaxel)
•Alcohol (chronic use, small fiber predominant; B1 deficiency, large and small fiber)
•Industrial solvents (e.g., hexane)
•Heavy metals (e.g., lead, arsenic)
•Certain antibiotics (e.g., metronidazole, nitrofurantoin)

Below is a list of toxic agents associated with peculiar features ⬇️

2/x

A common misconception regarding the treatment of Guillain-Barré syndrome (GBS) is the idea that it can be categorized as either "IVIg responsive" or "resistant." The only two therapies that are effective for GBS—plasma exchange and intravenous immunoglobulin (IVIg)—do not change mortality rates or long-term disability outcomes. Yes, you read that correctly. Both treatments are quite expensive, and clinical trials have shown that, compared to placebo, they only lead to accelerated recovery, with no significant difference in disability at one year or mortality rates.

Some of you may think I’m crazy for repeatedly stating that "Time is Nerve," but I strongly believe this to be true. The variation in response to immunotherapy in GBS is most likely related to the timing of starting treatment for an individual patient's disease course. This is why it is crucial to initiate therapy as soon as possible. I believe that starting treatment early may change the trajectory for many patients on an individual level.

Research indicates that the neuropathic process in GBS begins several days before patients exhibit any symptoms. After antibodies have been deposited in the nerves and complement activation occurs, plasma exchange or IVIg cannot effectively treat the damage that has already taken place in the nerves. While these treatments may help prevent further injury caused by antibodies or complement/cytokines, they cannot reverse the damage that has already been activated. As a result, patients with severe GBS who present to the hospital within less than three days or who become unable to walk in that same timeframe are likely to require mechanical ventilation and face a poor prognosis.

1/x Recent trials have demonstrated that giving a second dose of IVIg or repeating PLEX in severe cases is futile. Additionally, administering PLEX followed by IVIg does not improve outcomes. There is no evidence that PLEX after IVIg may be beneficial to patients who have “not responded” to IVIg, plus the potential harm of PLEX and a massive waste of money of washing out all the IVIg recently infused. The @PNSociety1 GBS guideline recommends against all this.

onlinelibrary.wiley.com/doi/10.1111/en…

2/x

Good morning, #NeuroX; I hope you all are having a great week in the clinic and will not feel down learning that Dr. Peter Dyck could identify the etiology of 76% of the “idiopathic” neuropathies referred to him in the 1970s.

In this post, I break down one of my favorite papers of all time.

This is the second post in celebration of Dr. Dyck’s retirement. I will try to post two more next month to compensate for February (sorry, busy times here 😅).

1/x

onlinelibrary.wiley.com/doi/abs/10.100…
These were patients seen by Dr. Dyck and/or Dr. Ed Lambert only. Eighty percent of these patients were referred by neurologists. Each patient underwent a detailed history and examination, along with nerve conduction studies (NCS), electromyography (EMG), quantitative sensory testing (QST), cerebrospinal fluid (CSF) analysis, and, in some cases, nerve biopsy.

If the neuropathy phenotype indicated a potential inherited neuropathy, family members of the patients who might also have neuropathy were invited to the clinic for neurologic evaluations, EMG, QST, and, in certain cases, nerve biopsy. If no family members had a history of neuropathy, parents, siblings, and children were invited to the clinic for the same evaluations.

2/x

The lumbosacral plexus plays a vital role in motor, sensory, and autonomic innervation of the lower limbs and pelvic region.

Lumbosacral plexopathies are not easy to diagnose, and below, I try to simplify how to approach them.

The main focus of this post is clinical features and diagnosis, but we will also touch on anatomy and treatment.

The temporal profile (TEMPO) is critical when assessing lumbosacral plexopathies. We divide them based on the time from symptom onset to nadir in hyperacute (< 24 hours), acute/subacute (1-30 days), and chronic (> 1 month).  The hyperacute causes are usually traumatic or vascular, which could be ischemic or compressive, secondary to retroperitoneal hematoma.  The acute/subacute causes are usually inflammatory (lumbosacral radiculoplexus neuropathies-LRPN) or infectious (syphilis, CMV, or VZV).  The chronic etiologies are usually inflammatory, radiation-induced, or neoplastic.

The most common causes of lumbosacral plexopathies I see in my practice are LRPN and radiation-induced plexopathies. Given my very specialized clinic, I also see very rare causes, like paraneoplastic, focal CIDP, and neurolymphomatosis, so I approach all of them the same way.

1/x
The lumbosacral plexus originates from the ventral rami of the L1-S4 nerve roots and consists of two main sections: the upper lumbar plexus and the lower lumbosacral plexus. The upper section is formed by the L1-L4 nerve roots, occasionally with input from the T12 root. Meanwhile, the lower section is derived from the L4-S4 nerve roots. Like the brachial plexus, structural variations, such as prefixed or postfixed configurations, are often observed. Anatomically, the plexus is embedded within the psoas major muscle and emerges from its lateral border. It provides motor and sensory innervation to the lower limb and pelvic region on the same side.

2/x

When I have a new fellow or resident in our peripheral nerve clinic, I always teach them the importance of defining the neuropathy clinical syndrome. NCS/EMG are valuable, but the neurological exam is the most important (as it should be in neurology but many have forgotten).

This is the neuropathy clinical phenotype classification I find the most helpful:

- Isolated small fiber neuropathy
- Length-dependent peripheral neuropathy (or distal symmetric polyneuropathy)
- Multiple mononeuropathies
- Mononeuropathy
- Asymmetric neuropathy
- Polyradiculoneuropathy
- Plexopathy (brachial or lumbosacral, many times a radiculoplexus neuropathy)
- Sensory neuronopathy
- Motor neuronopathy

I always tell my trainees they don’t have to memorize the causes of each phenotype. If you define the syndrome correctly, you can ask Google or ChatGtp what are the most likely causes. 😊

Definitions 👇👇👇

#NeuropathyBites

1/x Isolated Small Fiber Neuropathy

Pure small fiber neuropathy. Only temperature and pinprick dysfunction on exam. Ankle reflexes must be normal in patients < 60 yo. NCS must be normal for age.

2/x

Many of my neurology colleagues feel uneasy when admitting a patient with severe, chronic (> 2 months) rapidly progressive peripheral neuropathy of uncertain etiology. While there are more than 100 causes of neuropathy, the most likely causes in this clinical setting can be narrowed down to the six below:

🔺 Chronic Inflammatory Demyelinating Polyradiculoneuropathy (CIDP), including autoimmune nodopathies

🔺 Amyloidosis

🔺 Paraneoplastic syndrome, including POEMS syndrome

🔺 Vasculitis, including radiculoplexus neuropathies

🔺 Lymphoma or carcinomatous meningitis

🔺 Nutritional deficiencies

#NeuropathyBites
#NeuroTwitter
#MedTwitter
#MedX

1/x It’s important to note that this post refers to patients with moderate to severe disability caused by neuropathy, often dependent on wheelchairs and doesn't include patients with multifactorial gait disorder. In addition, some electromyographers report “severe neuropathy” based solely on lower extremities conduction studies, so caution is advised when using nerve conductions to define the severity of a neuropathy.

Another critical point is that patients are not good at differentiating progression versus no improvement of subacute/chronic weakness, so use landmarks like starting gait aids, the ability to stand up from the toilet without using the hands or help of someone, and falls, foot drop, wrist drop, abnormal gait, or inability to do something in their daily routine when they started. Be mindful that GBS, by definition, does not progress beyond 4 weeks.

Amyotrophic Lateral Sclerosis (ALS) is a more common cause of hospital admissions than all the conditions listed above, so a thorough history and detailed examination of the patient are essential. Bulbar symptoms/signs and upper motor neuron signs are highly suggestive of ALS. Moreover, up to 20% of ALS patients may also exhibit concomitant peripheral neuropathy; therefore, be careful about “motor-predominant polyradiculoneuropathies” that present with only mild sensory involvement.

2/x

In celebration of the legendary career of Professor Peter J. Dyck, who officially retired last month, I kick off today this series with a hidden gem: The 10 P's in the characterization and differential diagnosis of peripheral neuropathy.

#NeuropathyClassics

#DyckPapers

1/
Modern medical educators may not agree with a 10 point mnemonic but this was the 80s/90s and Dr. Dyck is a very thoughtful and comprehensive neurologist.

neurology.org/doi/10.1212/WN…

The first “P” (P1) is for Pattern:

- Anatomical and temporal localization of the disease.

- Anatomical pattern includes mononeuropathy, monoradiculopathy, multiple mononeuropathies, plexopathy, polyneuropathy or polyradiculoneuropathy.

- Temporal pattern considers onset (acute, subacute, chronic) and course (monophasic, recurrent,
progressive).

2/

Acute nutritional axonal neuropathy (dry beri-beri) is more common than many believe.

In patients with malnutrition, intractable vomiting, heavy alcohol use, or a poorly balanced diet, this condition is more likely than Guillain-Barré Syndrome (GBS). #NeuropathyBites

1/ These patients need IVT(thiamine) and not IVIg. I treat them with 500 mg IV q8h for 3 days, then 100 mg daily orally, and supplement other vitamins as needed.

The neuropathy is usually more distal and sensory predominant compared to GBS, though it can mimic GBS exactly.

2/

🚨Check out our latest work on vasculitic myopathy @GreenJournal! A fantastic collaboration between @MayoClinicNeuro and #MayoRheum. Thank you, @ElieNaddaf3, for the incredible mentorship, and @MdWarrington and #MattKoster for the help. Breakdown ⬇️ 1/7
neurology.org/doi/pdf/10.121… • We report 25 patients vasculitic myopathy

• Primary systemic Vasculitis: 40% (ANCA vasculitides most common)

• Secondary systemic vasculitis: 48% (RA most common)

• Nonsystemic vasculitic myopathy: 12%

2/7

Feels so good to be back to #Neurology. Today I had the pleasure to give #Neurologymorningreport on Necrotizing Autoimmune Myopathy #NAM. #MedTwitter follow below a few pearls I shared with the team @ErsidaBuraniqi @nzalewski2. THREAD. #NAM is an autoimmune myopathy characterized by severe proximal weakness, myofiber necrosis with minimal or no inflammatory infiltrates on muscle biopsy, and infrequent extra-muscular involvement.