[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Peripheral nerve and skeletal muscle](https://durgical.com/en/general-pathology/areas/nerve-muscle/) › Infectious neuropathies: leprosy, diphtheria, zoster

# Infectious neuropathies: leprosy, diphtheria, zoster

- Lesion

Some microbes live in nerves (leprosy), some poison myelin (diphtheria), and some hide in nerve ganglia and come back (shingles).

Updated Nov 12, 2026

## Key points

- Leprosy: anaesthetic skin patches and thickened peripheral nerves (ulnar, common fibular, great auricular); M. leprae grows best at cool temperatures.
- Tuberculoid (Th1): few lesions, granulomas destroy nerves, few bacilli. Lepromatous (Th2 or weak cellular immunity): diffuse lesions, foamy macrophages full of acid-fast bacilli.
- Diphtheria: exotoxin blocks protein synthesis in Schwann cells, causing demyelination weeks after infection; palatal paralysis and blurred vision first.
- Herpes zoster: painful vesicular rash in one dermatome; ganglion shows inflammation and neuronal loss; postherpetic neuralgia.
- HIV: distal symmetric painful sensory polyneuropathy; also GBS-like early, mononeuritis multiplex, CMV polyradiculopathy late.
- Lyme: facial nerve palsy (sometimes bilateral), painful radiculitis, meningitis.

## What it is

Infections damage peripheral nerves in several ways. Mycobacterium leprae invades Schwann cells of cool superficial nerves; the host's immune response decides the form, from few-lesion tuberculoid leprosy with granulomas that destroy nerves, to lepromatous leprosy with nerves full of bacilli. Leprosy still occurs in Colombia and is a leading infectious cause of neuropathy worldwide. Diphtheria toxin causes demyelination, beginning with palatal and eye muscles. Varicella-zoster virus remains latent in sensory ganglia and reactivates as shingles. HIV causes distal painful polyneuropathy and other forms; Lyme disease causes facial palsy and radiculoneuritis; CMV causes polyradiculopathy in advanced AIDS.

## Structure

- Tuberculoid leprosy: epithelioid granulomas within and around nerves, destroying them; acid-fast bacilli hard to find.
- Lepromatous leprosy: sheets of foamy macrophages (lepra cells) and Schwann cells packed with acid-fast bacilli (Fite stain); nerves thicken and fibrose.
- Diphtheria: segmental demyelination without much inflammation, starting near the dorsal root ganglia.
- Zoster: haemorrhagic inflammation of the sensory ganglion, Cowdry A inclusions, neuronal loss and later fibrosis.

## Step by step

- M. leprae enters Schwann cells by binding laminin-2 and dystroglycan of the basal lamina.
- The bacilli multiply slowly in cool nerves of the skin and limbs.
- A strong Th1 response forms granulomas that clear bacilli but destroy nerve (tuberculoid).
- A weak cellular response lets bacilli fill macrophages and nerves (lepromatous); immune reactions can flare later.
- Loss of sensation leads to painless injuries, ulcers, infections and resorption of fingers and toes.

## Leprosy at the two poles

| Feature | Tuberculoid | Lepromatous |
| --- | --- | --- |
| [Immune response](https://durgical.com/en/conditions/leprosy/) | Strong Th1 (IFN-γ, IL-2) | Weak cellular, Th2-type |
| Skin lesions | Few, well-defined, anaesthetic | Many, nodular, symmetric; leonine face |
| Bacilli | Few | Very many |
| Nerve pathology | Granulomas destroy nerves early | Bacilli-filled Schwann cells and macrophages |
| Lepromin skin test | Positive | Negative |

## Clinical notes

- Leprosy is curable with multidrug therapy, and early treatment prevents deformity; Colombia still reports new cases each year.
- Diphtheria is prevented by vaccination; the neuropathy appears weeks after the throat infection.
- Antiviral treatment of zoster in the first days lowers pain; vaccination reduces the risk of zoster and postherpetic neuralgia.

## Memory aid

Leprosy loves the cold and the Schwann cell; tuberculoid fights and burns the nerve, lepromatous lets the bacilli move in.

## Test yourself

Think of the answer, then tap the question to see it.

## Which cell does Mycobacterium leprae invade in nerves?

The Schwann cell.

## How do tuberculoid and lepromatous leprosy differ in immunity?

Tuberculoid has a strong Th1 response with granulomas and few bacilli; lepromatous has weak cellular immunity and many bacilli.

## How does diphtheria toxin cause neuropathy?

It blocks protein synthesis in Schwann cells, producing demyelination.

## Where does varicella-zoster virus stay latent?

In sensory ganglia (dorsal root and cranial nerve ganglia).

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## Elsewhere in DurgiPedia

- [Th1, Th2, Th17, Tfh and Treg](https://durgical.com/en/immunology/th1-th2-th17-tfh-and-treg/)

## Connections

## Related 4

- [Peripheral nerve injury: axonal vs demyelinating](https://durgical.com/en/general-pathology/peripheral-nerve-injury-axonal-vs-demyelinating/)
- [Guillain–Barré syndrome and CIDP](https://durgical.com/en/general-pathology/guillain-barre-syndrome-and-cidp/)
- [Granulomatous inflammation: caseating vs non-caseating, the causes to know](https://durgical.com/en/general-pathology/granulomatous-inflammation-caseating-vs-non-caseating-the-causes-to-know/)
- [Viral encephalitis: the shared pattern](https://durgical.com/en/general-pathology/viral-encephalitis-the-shared-pattern/)

## Related conditions 6

- [Leprosy (Hansen disease)](https://durgical.com/en/conditions/leprosy/)
- [Diphtheria](https://durgical.com/en/conditions/diphtheria/)
- [Herpes zoster (shingles)](https://durgical.com/en/conditions/herpes-zoster/)
- [HIV infection and AIDS](https://durgical.com/en/conditions/hiv-infection-and-aids/)
- [Lyme disease](https://durgical.com/en/conditions/lyme-disease/)
- [Cytomegalovirus infection](https://durgical.com/en/conditions/cytomegalovirus-infection/)

## Microorganisms 4

- [Mycobacterium leprae](https://durgical.com/en/microbiology/mycobacterium-leprae/)
- [Corynebacterium diphtheriae](https://durgical.com/en/microbiology/corynebacterium-diphtheriae/)
- [Varicella-zoster virus](https://durgical.com/en/microbiology/varicella-zoster-virus/)
- [Human immunodeficiency virus](https://durgical.com/en/microbiology/human-immunodeficiency-virus/)

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Leprosy](https://www.who.int/news-room/fact-sheets/detail/leprosy) (World Health Organization, 2025); [Diphtheria](https://www.who.int/news-room/fact-sheets/detail/diphtheria) (World Health Organization, 2025); [Herpes Zoster](https://www.ncbi.nlm.nih.gov/books/NBK441824/) (StatPearls (NCBI Bookshelf), 2025).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/general-pathology/infectious-neuropathies-leprosy-diphtheria-zoster/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/infectious-neuropathies-leprosy-diphtheria-zoster/