Paronychia (Acute & Chronic)

Two diseases in one fold. Paronychia is the most common hand infection, and it is two distinct entities. Acute bacterial paronychia is rapid, usually confined to a single digit, and follows a breach of the cuticle seal. Chronic paronychia lasts over 6 weeks and typically involves several digits of a "wet hand".

Who gets which. Acute disease most often affects otherwise healthy people with a recent nail-fold breach. Chronic disease clusters in "wet-hand" occupations (cleaners, bartenders, dishwashers, food handlers, swimmers) and is more common in diabetes, immunosuppression and with systemic retinoid use. Its peak is in middle-aged women in wet work.

The look-alikes. Recognising which entity you are facing, and separating the felon and the herpetic whitlow from it, drives the entire management. Where the problem sits tells you whether, and how, to cut:

• Nail fold with pus: acute paronychia. Drain it.
• Tense pulp: felon. A closed-space abscess of the volar fingertip, which needs a different incision (volar or high-lateral) to avoid skin necrosis and osteomyelitis.
• Grouped vesicles: herpetic whitlow. A viral (HSV) infection. Do not incise it.

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The perionychium. The soft tissue around the nail comprises the eponychium (the proximal nail fold, or cuticle), the paronychium (the lateral nail folds) and the hyponychium (the seal under the distal free edge). The germinal matrix lies beneath the proximal fold, and it is the structure to spare during drainage if permanent nail deformity is to be avoided.

Why pus runs around. The eponychial fold continues as a thin layer over the germinal matrix. That continuity lets pus in one lateral fold spread proximally under the eponychium and across to the other fold, which is the run-around (horseshoe) abscess.

The seal and its breach. The seal between the cuticle and the nail plate is the principal barrier. Once it is breached by a hangnail, nail-biting, an aggressive manicure, a splinter or other minor trauma, or an ingrowing nail, bacteria enter the potential space of the nail fold.

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Acute: the organisms. Staphylococcus aureus is the most common organism. MRSA is increasingly frequent and should be assumed in non-responders and in high-prevalence settings. Mixed flora also occur: streptococci, and in nail-biters or with oral contact, anaerobes and Eikenella corrodens.

Acute: the course. Infection begins as a cellulitis of the fold and, if untreated, localises into an abscess that points at the fold margin or under the eponychium, the pus collecting superficial to the nail plate. Untreated pus can track under the nail (a subungual abscess) or around the base (a run-around abscess), and rarely into the pulp or to the distal phalanx.

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Chronic: a dermatitis of the barrier. Chronic paronychia is not primarily an abscess. It is a chronic inflammatory, eczematous dermatitis of the nail fold, driven by repeated exposure to moisture and irritants (detergents, food, alkalis). Loss of the protective cuticle lets irritants and microbes, notably Candida albicans and bacteria, enter and perpetuate the inflammation, and the chronic inflammation damages the germinal matrix to produce nail dystrophy.

Candida is a coloniser. Candida is best regarded as a coloniser and a marker of the barrier defect rather than the sole pathogen. That is why antifungals alone often underperform compared with treating the underlying dermatitis.

The pulp is a different space. The felon's pulp is divided by ~15 to 20 fibrous septa running from the periosteum of the distal phalanx to the skin, creating tight, fat-filled compartments. Infection, usually S. aureus and often after a splinter or penetrating injury, raises the pressure within these closed spaces. The complications of that closed-space pressure are:

• skin and pulp necrosis
• distal phalanx osteomyelitis
• septic DIP arthritis
• spread to the flexor sheath
• tip ischaemia

Acute paronychia. Onset is rapid, over hours to days, and usually in one digit: throbbing pain, erythema and swelling of a single nail fold, with a visible collection of pus at the fold margin or under the cuticle. There is often one of the precipitants above. Fluctuance and a "shiny", tense fold indicate a drainable abscess.

Chronic paronychia. Onset is insidious, often in several digits of the dominant hand. The cuticle is lost and the fold is boggy or retracted, with intermittent discharge and episodic acute flares superimposed on the chronic change. The nail is dystrophic: transverse ridging, discolouration and surface irregularity.

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Felon. A rapidly worsening, throbbing, tense, exquisitely tender and globally swollen distal pulp, distal to the DIP crease. The rest of the finger is spared, whereas a paronychia is confined to the nail fold.

Herpetic whitlow. Grouped vesicles on an erythematous base, severe pain out of proportion and a recurrent history point to HSV rather than bacterial paronychia.

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What to examine for. Assess how much pus there is and where it sits: lateral fold, eponychium, subungual or run-around. Look for spread to the pulp (a felon), and for lymphangitis or systemic upset. Always look for vesicles before reaching for a blade.

The mimics. A chronic, non-healing or atypical single-digit "paronychia" that resists treatment should make you think of the mimics:

• squamous cell carcinoma
• amelanotic melanoma
• pyogenic granuloma
• chronic osteomyelitis
• gout (tophi)
• sarcoid
• unusual organisms: mycobacteria, or Candida in the immunosuppressed

A clinical diagnosis. Paronychia is diagnosed clinically, and investigations are selective.

Acute disease. The pus is swabbed at drainage, and everything else is conditional:

• Gram stain and culture/sensitivity of the pus, which guides antibiotics and detects MRSA
• A radiograph, not routine, if there is a suspected foreign body or retained splinter, or chronicity or possible osteomyelitis of the distal phalanx
• Bloods only if the patient is systemically unwell, immunocompromised or diabetic

Chronic or atypical disease. The biopsy is the key safety net:

• Fungal and bacterial microscopy and culture (KOH, Candida)
• HbA1c or glucose, and a review of immunosuppression, in recurrent disease
• Biopsy of any chronic, atypical or non-resolving single-digit lesion, to exclude malignancy (SCC, melanoma) and granulomatous or unusual infection
• Tzanck smear or viral PCR if herpetic whitlow is suspected

The governing principle. No pus, no knife — but once there is pus, drain it. Early acute paronychia (cellulitis only) may settle with warm soaks and oral antibiotics. An established abscess requires drainage: antibiotics alone fail once pus is present, and they are an adjunct, not a substitute. Chronic paronychia is treated as a dermatitis, with moisture avoidance and topical anti-inflammatories, and repeated incision is the wrong treatment.

Acute — drain the pusChronic — treat the barrierFelon — decompress the pulpHerpetic whitlow — don't incise

Early: cellulitis, no abscess. Warm soaks, elevation and a short course of an anti-staphylococcal oral antibiotic such as flucloxacillin. Cover MRSA (co-trimoxazole, doxycycline or clindamycin, per local sensitivities) where it is prevalent or in non-responders. Many early cases resolve without surgery.

Established abscess: drain where the pus sits. Every technique is done under a digital (ring) block and spares the germinal matrix:

• Simple elevation, for pus at a lateral fold. Slide a blunt elevator (Freer) or a blade held parallel to the nail under the affected fold to lift it off the plate and release the pus, or make a small incision at the point of maximal fluctuance, directed away from the eponychium.
• Eponychial flap (single or double incision), for pus under the eponychium or proximal fold. One or two short longitudinal incisions at the corner(s) of the fold let it be reflected proximally to expose and drain the proximal nail; never incise transversely across the matrix.
• Partial nail removal (the proximal third) for subungual pus localised proximally, or complete nail removal for extensive subungual pus, to deroof the collection.
• Run-around (horseshoe) abscess, where pus has tracked under the nail base or to the opposite fold. It will recur unless the eponychial fold is elevated, with partial or complete nail removal. For a severe run-around, the "Swiss roll" technique incises both eponychial corners, reflects the fold and rolls it back over a suture or dressing, leaving it open to drain and unrolling it later; it drains the whole horseshoe while preserving the nail and matrix.

Leave the wound open or lightly packed, with a dressing and soaks afterwards. Inadequate drainage is the usual reason for recurrence.

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The cardinal error. Over-zealous incision near the proximal fold, a deep or transverse cut into the germinal matrix, leaves permanent nail dystrophy.

Antibiotics as adjunct. Reserve or continue oral antibiotics for surrounding cellulitis, lymphangitis or systemic features, or for the immunocompromised or diabetic patient, and tailor them to culture. They do not replace adequate drainage.

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First line: the barrier. The cornerstone is avoidance of moisture and irritants: keep the hands dry, wear cotton-lined waterproof gloves for wet work, stop nail-biting and manicures, and use emollients. Treat any underlying diabetes.

Then the dermatitis. A topical corticosteroid for the inflammatory dermatitis is at least as effective as, and often better than, systemic antifungals (randomised evidence: Tosti 2002). Add a topical antifungal or anti-yeast agent if Candida is implicated.

Refractory disease. Options include a course of systemic antifungal if Candida is confirmed and, in selected chronic cases, eponychial marsupialisation: excision of a crescent of skin over the proximal fold to allow drainage and re-establish a seal, with or without nail removal. Always biopsy the persistent atypical single-digit lesion before assuming benign disease.

Mnemonic

WETChronic paronychia

W

Wet hands → chronic paronychia (cleaners, bartenders, food handlers)

E

Eczematous/inflammatory → treat as dermatitis (barrier + topical steroid)

T

Think malignancy → biopsy the chronic, atypical, single-digit lesion

Hook:Chronic paronychia lives on WET hands — dry them, calm the inflammation, and don't miss a tumour.

The incision. Drain through a high lateral (mid-axial) incision over the point of maximal tenderness, on the non-contact border (ulnar in the fingers, radial in thumb/index), or through a longitudinal volar incision, breaking the septa to decompress the pulp.

What to avoid. Do not cross the DIP flexion crease (contracture). Do not make a "fish-mouth" or through-and-through incision, which causes an unstable, anaesthetic, painful pad and tip necrosis. Antibiotics are adjunctive; X-ray if osteomyelitis is suspected.

Herpetic whitlow — do not incise

Incision is contraindicated. It offers no benefit and risks bacterial superinfection and viral spread, including to the surgeon. The infection is self-limiting: manage it with analgesia and a protective dressing, and consider aciclovir, which is most useful if started early or in recurrent or immunocompromised cases.

Of the disease. Inadequate or late drainage leaves a run-around (horseshoe) abscess, and infection can spread to the pulp (felon), the flexor sheath or the distal phalanx (osteomyelitis). Chronic disease leaves nail dystrophy and permanent matrix damage. Recurrence often comes from persistent moisture exposure or missed subungual pus.

Of treatment. Germinal matrix injury from an over-zealous incision near the eponychium causes permanent nail deformity. Inadequate drainage leads to persistence or recurrence, and antibiotic overuse without drainage is an error of its own. The dangerous error is the missed mimic, an SCC or melanoma treated repeatedly as "infection".