Psoriatic arthritis

Psoriatic arthritis

Polyarticular arthritis
Skin disease: Psoriasis (Skin rash)
Chronic inflammatory
40yo, Caucasian
?Factors involved: Genetic, Immune system, Environmental
HLA-B27 +ve in 60%

Hand:
- Most commonly involved skeleton
- Interphalangeal joint (PIJ, DIJ)
- 'Fluffy periostitis'
- Bony proliferation*
- Joint erosion from articular margin* to centrally.
- Tapering of one end, saucerisation of the other end of the articular surface: Pencil-in-cup deformity
- Preserved bony mineralisation (no osteopenia), ivory phalanx
- Ankylosis
- Diffuse soft tissue swelling: Sausage digit

SIJs:
- Asymmetric sacroiliitis, sclerosis, large erosion
- Ankylosis is UNcommon

Vertebra:
- More commonly involved in MALE
- Asymmetric
- Atlanto-axial subluxation
- Squarring of vertebrae
- Enthesitis: comma-shaped ossification, paravertebral (parasyndesmophytes)
- Thoracolumbar region

Others:
- MTPJ
- TA insertion of the Calcaneum: Fluffy periostitis & Erosion

*HALLMARKS for Psoriatic arthritis

DDx:
- Ankylosing spondylitis (Ossification less bulky, symmetric sacroiliitis)
- Reactive arthritis (Genitourinary symptoms)
- Hyperparathyroidism (similarity: presence of large SIJ erosion)

Modic changes in MRI

Modic classification

Use for different endplate marrow degenerative changes (which is postulated to result from same pathological process, but at different stages) in lumbar spine MR imaging.

Modic degenerative changes often accompanies disk degenerative disease (DDD)

The Modic change can be of mix type 1 and 2, type 2 and 3.

Modic type	T1w	T2w	Pathology
1 (oedema)	Hypointense	Hyperintense Modic1. Note also disk dessication.	Oedema & Inflammation
2 (fat)	Hyperintense	Iso/Slight Hyperintense Modic2. Note also disk dessication.	Marrow ischaemia, thus red marrow converts to fatty yellow marrow
3 (sclerosis)	Hypointense	Hypointense Modic3. Note also disk dessication.	Subchondral sclerosis Radiograph of the same patient with Modic 3 degeneration. Note sclerosis (arrow).

Note:

Disciitis can mimic Modic 1 degenerative change, when the adjacent bone marrows from the inflamed/infected disk is inflamed

Look at 3 things:
(1) Whether the intervertebral disk shows corresponding degenerative change (disk dessication) or shows inflammed (disciitis)

(2) Whether the bone or adjacent structures points to infection eg bone erosion, abscess formation

(3) Last but not least, correlate clinically - Lab changes, Clinical history

	Endplates	Intervertebral disk	Others
Modic 1	Low T1w, High T2w	Iso/Low T2w Usually dessicated (modic change accompanies disk degenerative disease)	Clinically non-toxic
Diskiitis	Same as above, but with features of diskiitis ie bone erosion	High T2w Inflammed disk	Presence of inflammation / abscess in adjacent structures (eg paraspinal, epidural abscess) Clinical and laboratory findings of infection