is riedel thyroiditis also subacute thyroiditis

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No, Riedel thyroiditis is not subacute thyroiditis. They are entirely separate conditions. Here is a clear breakdown:

Types of Thyroiditis - Where Riedel Fits

The major thyroiditides are classified as follows:

Type	Also Known As	Character	Cause
Hashimoto thyroiditis	Chronic lymphocytic thyroiditis	Autoimmune, lymphoplasmacytic infiltrate	Autoimmune
Subacute granulomatous thyroiditis	de Quervain thyroiditis	Painful, self-limited, granulomatous	Post-viral
Subacute lymphocytic thyroiditis	Painless/silent/postpartum thyroiditis	Painless, self-limited, lymphocytic	Autoimmune
Riedel thyroiditis	Riedel struma / chronic fibrous thyroiditis	Dense fibrosis, invasive, very rare	Unknown (autoimmune or multifocal fibrosclerosis)
Acute suppurative thyroiditis	Infectious thyroiditis	Bacterial abscess	Bacterial infection

Riedel Thyroiditis - Key Features

What it is: An extremely rare inflammatory process causing diffuse destruction and fibrosis of the thyroid gland - Sabiston Textbook of Surgery
Hallmark: The gland becomes rock-hard ("woody") and the fibrotic process extends into surrounding structures - trachea, recurrent laryngeal nerve, esophagus - causing airway obstruction, dysphagia, and dysphonia
Associations: Linked to other fibrosing conditions (multifocal fibrosclerosis) such as retroperitoneal fibrosis, sclerosing cholangitis, and chronic mediastinitis
Thyroid function: Leads to hypothyroidism
Histology: Dense fibrous replacement of thyroid parenchyma - non-granulomatous
Treatment: Corticosteroids, tamoxifen, mycophenolate, rituximab; surgery (isthmus wedge resection) for tracheal decompression or to rule out anaplastic carcinoma

Subacute Thyroiditis (de Quervain) - Key Features

What it is: A self-limited, usually post-viral granulomatous inflammation - Robbins Basic Pathology
Hallmark: Painful, tender thyroid; often preceded by upper respiratory tract infection
Histology: Granulomas with giant cells - completely opposite to Riedel's fibrosis
Course: Transient thyrotoxicosis → euthyroid → possible temporary hypothyroidism → recovery
Treatment: NSAIDs, steroids for severe pain; self-resolves

Why the Confusion Sometimes Arises

The term "subacute" is applied to two different thyroiditis types:

Subacute granulomatous (de Quervain) - painful
Subacute lymphocytic (silent/postpartum) - painless

Riedel thyroiditis is classified as chronic fibrous thyroiditis and belongs to neither subacute category. Some older classification schemes listed it alongside "chronic" thyroiditides (like Hashimoto's), but it is pathologically distinct from all of them.

In short: Riedel = chronic + fibrosing + invasive; Subacute = transient + inflammatory (either granulomatous or lymphocytic).

tell me all subacute thyroiditis examples

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Here are all the recognized subacute thyroiditis examples, sourced from textbooks:

Subacute Thyroiditis - All Types

The term "subacute" in thyroiditis is used in two distinct ways - as a specific disease name and as a histological descriptor. This creates some overlap in terminology.

1. Subacute Granulomatous Thyroiditis (de Quervain Thyroiditis)

This is what most people mean by "subacute thyroiditis"

Other names: de Quervain thyroiditis, giant cell thyroiditis, painful subacute thyroiditis
Cause: Post-viral (preceded by upper respiratory infection in most patients)
Presentation: Painful, tender thyroid; fever; malaise; neck pain worsens with swallowing
Histology: Granulomas with multinucleated giant cells engulfing extravasated colloid; follicle destruction
Course: Transient hyperthyroidism → euthyroid → possible transient hypothyroid → full recovery (self-limited, resolves in 6-8 weeks)
ESR: Markedly elevated
Treatment: NSAIDs; corticosteroids for severe cases - Robbins Basic Pathology

2. Subacute Lymphocytic Thyroiditis (Silent / Painless Thyroiditis)

Also called "subacute" due to its histological pattern

Other names: Painless thyroiditis, silent thyroiditis, lymphocytic thyroiditis with spontaneously resolving hyperthyroidism
Cause: Autoimmune (considered a variant of Hashimoto thyroiditis); circulating antithyroid antibodies present in most patients
Presentation: Painless neck mass or features of thyroid hormone excess - NO neck pain or tenderness
Histology: Lymphocytic infiltration (not granulomatous)
Course: Thyrotoxic phase → euthyroid within a few months; minority progress to permanent hypothyroidism
Affects: Mostly middle-aged women - Robbins Basic Pathology

3. Postpartum Thyroiditis

A subtype of subacute lymphocytic thyroiditis

What it is: Same pathology as silent thyroiditis, but onset follows pregnancy (within 1 year postpartum)
Cause: Autoimmune rebound after the immune suppression of pregnancy
Presentation: Painless; transient hyper- or hypothyroid phase
Histology: Lymphocytic infiltration
Course: Usually self-limited; some patients develop permanent hypothyroidism
Note: Classified together with painless thyroiditis in most textbook schemes - Tietz Textbook of Laboratory Medicine

Summary Table

Type	Pain	Histology	Cause	Course
Subacute granulomatous (de Quervain)	Yes - painful	Granulomas + giant cells	Post-viral	Self-limited, full recovery
Subacute lymphocytic (silent/painless)	No	Lymphocytic infiltrate	Autoimmune	Self-limited, some → hypothyroid
Postpartum thyroiditis	No	Lymphocytic infiltrate	Autoimmune (post-pregnancy)	Self-limited, some → permanent hypothyroid

Key Point on Terminology

The word "subacute" distinguishes these from:

Acute thyroiditis (bacterial/suppurative - rapid onset, severe infection)
Chronic thyroiditis (Hashimoto's, Riedel's - long-standing, often permanent changes)

Both granulomatous and lymphocytic forms are "subacute" because they run a weeks-to-months course and are generally self-resolving - Current Surgical Therapy.

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